diff --git a/config/tsconfig.base.json b/config/tsconfig.base.json
index ebcee5e168a..913426696dd 100644
--- a/config/tsconfig.base.json
+++ b/config/tsconfig.base.json
@@ -4,6 +4,7 @@
     "declaration": true,
     "importHelpers": true,
     "strictNullChecks": true,
+    "noImplicitAny": true,
     "lib": [
       "es2015",
       "dom"
diff --git a/packages/app/index.node.ts b/packages/app/index.node.ts
index fb68cb739c9..25d71972fe6 100644
--- a/packages/app/index.node.ts
+++ b/packages/app/index.node.ts
@@ -18,8 +18,11 @@
 import { FirebaseNamespace } from '@firebase/app-types';
 import { _FirebaseNamespace } from '@firebase/app-types/private';
 import { createFirebaseNamespace } from './src/firebaseNamespace';
+// Node specific packages.
+// @ts-ignore
 import Storage from 'dom-storage';
-import { XMLHttpRequest } from 'xmlhttprequest';
+// @ts-ignore
+import XMLHttpRequest from 'xmlhttprequest';
 
 const _firebase = createFirebaseNamespace() as _FirebaseNamespace;
 
diff --git a/packages/app/src/firebaseNamespaceCore.ts b/packages/app/src/firebaseNamespaceCore.ts
index e648e27034f..2067d602bf5 100644
--- a/packages/app/src/firebaseNamespaceCore.ts
+++ b/packages/app/src/firebaseNamespaceCore.ts
@@ -80,7 +80,8 @@ export function createFirebaseNamespaceCore(
   //
   //   import * as firebase from 'firebase';
   //   which becomes: var firebase = require('firebase');
-  namespace['default'] = namespace;
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  (namespace as any)['default'] = namespace;
 
   // firebase.apps is a read-only getter.
   Object.defineProperty(namespace, 'apps', {
@@ -108,6 +109,7 @@ export function createFirebaseNamespaceCore(
     return apps[name];
   }
 
+  // @ts-ignore
   app['App'] = firebaseAppImpl;
   /**
    * Create a new App instance (name must be unique).
@@ -196,6 +198,7 @@ export function createFirebaseNamespaceCore(
 
     // The Service namespace is an accessor function ...
     function serviceNamespace(appArg: FirebaseApp = app()): FirebaseService {
+      // @ts-ignore
       if (typeof appArg[name] !== 'function') {
         // Invalid argument.
         // This happens in the following case: firebase.storage('gs:/')
@@ -205,6 +208,7 @@ export function createFirebaseNamespaceCore(
       }
 
       // Forward service instance lookup to the FirebaseApp.
+      // @ts-ignore
       return appArg[name]();
     }
 
@@ -214,9 +218,11 @@ export function createFirebaseNamespaceCore(
     }
 
     // Monkey-patch the serviceNamespace onto the firebase namespace
+    // @ts-ignore
     namespace[name] = serviceNamespace;
 
     // Patch the FirebaseAppImpl prototype
+    // @ts-ignore
     firebaseAppImpl.prototype[name] = function(...args) {
       const serviceFxn = this._getService.bind(this, name);
       return serviceFxn.apply(this, allowMultipleInstances ? args : []);
diff --git a/packages/app/test/firebaseApp.test.ts b/packages/app/test/firebaseApp.test.ts
index 9d68fef5ad6..2ca8785f173 100644
--- a/packages/app/test/firebaseApp.test.ts
+++ b/packages/app/test/firebaseApp.test.ts
@@ -314,7 +314,10 @@ function executeFirebaseLiteTests(): void {
   });
 }
 
-function firebaseAppTests(testName, firebaseNamespaceFactory): void {
+function firebaseAppTests(
+  testName: string,
+  firebaseNamespaceFactory: () => FirebaseNamespace
+): void {
   describe(testName, () => {
     let firebase: FirebaseNamespace;
 
diff --git a/packages/database/index.node.ts b/packages/database/index.node.ts
index 7f695ba3eb8..71bcfa964ea 100644
--- a/packages/database/index.node.ts
+++ b/packages/database/index.node.ts
@@ -40,7 +40,11 @@ import * as types from '@firebase/database-types';
 
 const ServerValue = Database.ServerValue;
 
-export function initStandalone(app, url, version?: string) {
+export function initStandalone(
+  app: FirebaseApp,
+  url: string,
+  version?: string
+) {
   /**
    * This should allow the firebase-admin package to provide a custom version
    * to the backend
diff --git a/packages/database/src/core/PersistentConnection.ts b/packages/database/src/core/PersistentConnection.ts
index 37ed2d1ff62..44731a1b4d8 100644
--- a/packages/database/src/core/PersistentConnection.ts
+++ b/packages/database/src/core/PersistentConnection.ts
@@ -948,11 +948,14 @@ export class PersistentConnection extends ServerActions {
 
     // Puts depend on having received the corresponding data update from the server before they complete, so we must
     // make sure to send listens before puts.
-    forEach(this.listens_, (pathString: string, queries: Object) => {
-      forEach(queries, (key: string, listenSpec: ListenSpec) => {
-        this.sendListen_(listenSpec);
-      });
-    });
+    forEach(
+      this.listens_,
+      (pathString: string, queries: { [key: string]: ListenSpec }) => {
+        forEach(queries, (key: string, listenSpec: ListenSpec) => {
+          this.sendListen_(listenSpec);
+        });
+      }
+    );
 
     for (let i = 0; i < this.outstandingPuts_.length; i++) {
       if (this.outstandingPuts_[i]) this.sendPut_(i);
diff --git a/packages/database/src/core/snap/ChildrenNode.ts b/packages/database/src/core/snap/ChildrenNode.ts
index 196e5bff410..e57fdbeb8d2 100644
--- a/packages/database/src/core/snap/ChildrenNode.ts
+++ b/packages/database/src/core/snap/ChildrenNode.ts
@@ -201,7 +201,7 @@ export class ChildrenNode implements Node {
   val(exportFormat?: boolean): object {
     if (this.isEmpty()) return null;
 
-    const obj: { [k: string]: Object } = {};
+    const obj: { [k: string]: unknown } = {};
     let numKeys = 0,
       maxKey = 0,
       allIntegerKeys = true;
@@ -218,7 +218,7 @@ export class ChildrenNode implements Node {
 
     if (!exportFormat && allIntegerKeys && maxKey < 2 * numKeys) {
       // convert to array.
-      const array: Object[] = [];
+      const array: unknown[] = [];
       for (let key in obj) array[(key as any) as number] = obj[key];
 
       return array;
diff --git a/packages/database/src/core/snap/IndexMap.ts b/packages/database/src/core/snap/IndexMap.ts
index 624d66dcfee..0853dacb5ba 100644
--- a/packages/database/src/core/snap/IndexMap.ts
+++ b/packages/database/src/core/snap/IndexMap.ts
@@ -75,7 +75,7 @@ export class IndexMap {
       // regular child map
       return null;
     } else {
-      return sortedMap;
+      return sortedMap as SortedMap<NamedNode, Node>;
     }
   }
 
diff --git a/packages/database/src/core/snap/Node.ts b/packages/database/src/core/snap/Node.ts
index 052140e135f..de4960600ed 100644
--- a/packages/database/src/core/snap/Node.ts
+++ b/packages/database/src/core/snap/Node.ts
@@ -119,7 +119,7 @@ export interface Node {
    * @param {boolean=} exportFormat True for export format (also wire protocol format).
    * @return {*} Value of this node as JSON.
    */
-  val(exportFormat?: boolean): Object;
+  val(exportFormat?: boolean): unknown;
 
   /**
    * @return {string} hash representing the node contents.
diff --git a/packages/database/src/core/snap/nodeFromJSON.ts b/packages/database/src/core/snap/nodeFromJSON.ts
index 84fd3d0d34f..532916266de 100644
--- a/packages/database/src/core/snap/nodeFromJSON.ts
+++ b/packages/database/src/core/snap/nodeFromJSON.ts
@@ -113,7 +113,7 @@ export function nodeFromJSON(
     }
   } else {
     let node: Node = ChildrenNode.EMPTY_NODE;
-    const jsonObj = json as object;
+    const jsonObj = json as { [key: string]: unknown };
     forEach(jsonObj, (key: string, childData: any) => {
       if (contains(jsonObj, key)) {
         if (key.substring(0, 1) !== '.') {
diff --git a/packages/database/src/core/snap/snap.ts b/packages/database/src/core/snap/snap.ts
index b94a0d26c32..91eca450fa3 100644
--- a/packages/database/src/core/snap/snap.ts
+++ b/packages/database/src/core/snap/snap.ts
@@ -47,7 +47,8 @@ export const validatePriorityNode = function(priorityNode: Node) {
     assert(
       typeof val === 'string' ||
         typeof val === 'number' ||
-        (typeof val === 'object' && contains(val, '.sv')),
+        (typeof val === 'object' &&
+          contains(val as { [key: string]: unknown }, '.sv')),
       'Priority must be a string or number.'
     );
   } else {
diff --git a/packages/database/src/core/util/CountedSet.ts b/packages/database/src/core/util/CountedSet.ts
index 6ccc0576772..f88c8009f3d 100644
--- a/packages/database/src/core/util/CountedSet.ts
+++ b/packages/database/src/core/util/CountedSet.ts
@@ -22,7 +22,7 @@ import { isEmpty, getCount, forEach, contains } from '@firebase/util';
  *
  * @template K, V
  */
-export class CountedSet<K, V> {
+export class CountedSet<K extends string | number, V> {
   set: { [k: string]: V } = {};
 
   /**
@@ -38,7 +38,7 @@ export class CountedSet<K, V> {
    * @return {boolean}
    */
   contains(key: K) {
-    return contains(this.set, key);
+    return contains(this.set, key as string);
   }
 
   /**
@@ -82,8 +82,8 @@ export class CountedSet<K, V> {
    * Run a function on each k,v pair in the set
    * @param {function(K, V)} fn
    */
-  each(fn: (k: K, v: V) => void) {
-    forEach(this.set, (k: K, v: V) => fn(k, v));
+  each(fn: (k: K | string, v: V) => void) {
+    forEach(this.set, (k: string, v: V) => fn(k, v));
   }
 
   /**
@@ -92,8 +92,8 @@ export class CountedSet<K, V> {
    */
   keys(): K[] {
     const keys: K[] = [];
-    forEach(this.set, (k: K) => {
-      keys.push(k);
+    forEach(this.set, (k: string) => {
+      keys.push(k as K);
     });
     return keys;
   }
diff --git a/packages/database/src/core/util/Tree.ts b/packages/database/src/core/util/Tree.ts
index 97263db6979..00cded4c685 100644
--- a/packages/database/src/core/util/Tree.ts
+++ b/packages/database/src/core/util/Tree.ts
@@ -57,7 +57,7 @@ export class Tree<T> {
   subTree(pathObj: string | Path): Tree<T> {
     // TODO: Require pathObj to be Path?
     let path = pathObj instanceof Path ? pathObj : new Path(pathObj);
-    let child = this as any,
+    let child = this as Tree<T>,
       next;
     while ((next = path.getFront()) !== null) {
       const childNode = safeGet(child.node_.children, next) || new TreeNode();
diff --git a/packages/database/tsconfig.json b/packages/database/tsconfig.json
index 2260db9d56c..5d390b031c4 100644
--- a/packages/database/tsconfig.json
+++ b/packages/database/tsconfig.json
@@ -2,7 +2,8 @@
   "extends": "../../config/tsconfig.base.json",
   "compilerOptions": {
     "outDir": "dist",
-    "strictNullChecks": false
+    "strictNullChecks": false,
+    "noImplicitAny": false
   },
   "exclude": [
     "dist/**/*"
diff --git a/packages/firestore/index.node.ts b/packages/firestore/index.node.ts
index 413d4cf5f0f..1393181e72d 100644
--- a/packages/firestore/index.node.ts
+++ b/packages/firestore/index.node.ts
@@ -16,12 +16,13 @@
  */
 
 import firebase from '@firebase/app';
-import './src/platform_node/node_init';
+import { FirebaseNamespace } from '@firebase/app-types';
+import * as types from '@firebase/firestore-types';
 import { Firestore } from './src/api/database';
 import { configureForFirebase } from './src/platform/config';
-import * as types from '@firebase/firestore-types';
+import './src/platform_node/node_init';
 
-export function registerFirestore(instance) {
+export function registerFirestore(instance: FirebaseNamespace): void {
   configureForFirebase(instance);
 }
 
diff --git a/packages/firestore/index.ts b/packages/firestore/index.ts
index 841b76b8436..3070762f006 100644
--- a/packages/firestore/index.ts
+++ b/packages/firestore/index.ts
@@ -16,13 +16,14 @@
  */
 
 import firebase from '@firebase/app';
-import './src/platform_browser/browser_init';
+import { FirebaseNamespace } from '@firebase/app-types';
 import { Firestore } from './src/api/database';
 import { configureForFirebase } from './src/platform/config';
+import './src/platform_browser/browser_init';
 
 import * as types from '@firebase/firestore-types';
 
-export function registerFirestore(instance) {
+export function registerFirestore(instance: FirebaseNamespace): void {
   configureForFirebase(instance);
 }
 
diff --git a/packages/firestore/src/api/credentials.ts b/packages/firestore/src/api/credentials.ts
index 883d5248675..8346f4b577b 100644
--- a/packages/firestore/src/api/credentials.ts
+++ b/packages/firestore/src/api/credentials.ts
@@ -263,7 +263,7 @@ export class FirstPartyToken implements Token {
   constructor(private gapi: Gapi, private sessionIndex: string) {}
 
   get authHeaders(): { [header: string]: string } {
-    const headers = {
+    const headers: { [header: string]: string } = {
       'X-Goog-AuthUser': this.sessionIndex
     };
     const authHeader = this.gapi.auth.getAuthHeaderValueForFirstParty([]);
@@ -309,8 +309,8 @@ export function makeCredentialsProvider(
 
   switch (credentials.type) {
     case 'gapi':
-      const client = credentials.client;
-      // Make sure this is a Gapi client.
+      const client = credentials.client as Gapi;
+      // Make sure this really is a Gapi client.
       assert(
         !!(
           typeof client === 'object' &&
@@ -321,7 +321,7 @@ export function makeCredentialsProvider(
         'unexpected gapi interface'
       );
       return new FirstPartyCredentialsProvider(
-        client as Gapi,
+        client,
         credentials.sessionIndex || '0'
       );
 
diff --git a/packages/firestore/src/core/firestore_client.ts b/packages/firestore/src/core/firestore_client.ts
index 2d243410593..db7ca678107 100644
--- a/packages/firestore/src/core/firestore_client.ts
+++ b/packages/firestore/src/core/firestore_client.ts
@@ -60,7 +60,7 @@ import { AutoId } from '../util/misc';
 import { DatabaseId, DatabaseInfo } from './database_info';
 import { Query } from './query';
 import { Transaction } from './transaction';
-import { OnlineStateSource } from './types';
+import { OnlineState, OnlineStateSource } from './types';
 import { ViewSnapshot } from './view_snapshot';
 
 const LOG_TAG = 'FirestoreClient';
@@ -429,12 +429,16 @@ export class FirestoreClient {
           serializer
         );
 
-        const remoteStoreOnlineStateChangedHandler = onlineState =>
+        const remoteStoreOnlineStateChangedHandler = (
+          onlineState: OnlineState
+        ) =>
           this.syncEngine.applyOnlineStateChange(
             onlineState,
             OnlineStateSource.RemoteStore
           );
-        const sharedClientStateOnlineStateChangedHandler = onlineState =>
+        const sharedClientStateOnlineStateChangedHandler = (
+          onlineState: OnlineState
+        ) =>
           this.syncEngine.applyOnlineStateChange(
             onlineState,
             OnlineStateSource.SharedClientState
diff --git a/packages/firestore/src/core/sync_engine.ts b/packages/firestore/src/core/sync_engine.ts
index 6c25992dab3..a00161ee1ae 100644
--- a/packages/firestore/src/core/sync_engine.ts
+++ b/packages/firestore/src/core/sync_engine.ts
@@ -433,7 +433,9 @@ export class SyncEngine implements RemoteSyncer, SharedClientStateSyncer {
         objUtils.forEach(
           remoteEvent.targetChanges,
           (targetId, targetChange) => {
-            const limboResolution = this.limboResolutionsByTarget[targetId];
+            const limboResolution = this.limboResolutionsByTarget[
+              Number(targetId)
+            ];
             if (limboResolution) {
               // Since this is a limbo resolution lookup, it's for a single document
               // and it could be added, modified, or removed, but not a combination.
diff --git a/packages/firestore/src/local/indexeddb_mutation_queue.ts b/packages/firestore/src/local/indexeddb_mutation_queue.ts
index 4e3a8333563..2ddfaff34a4 100644
--- a/packages/firestore/src/local/indexeddb_mutation_queue.ts
+++ b/packages/firestore/src/local/indexeddb_mutation_queue.ts
@@ -476,9 +476,15 @@ export class IndexedDbMutationQueue implements MutationQueue {
       batch
     ).next(removedDocuments => {
       this.removeCachedMutationKeys(batch.batchId);
-      return PersistencePromise.forEach(removedDocuments, key => {
-        return this.referenceDelegate.removeMutationReference(transaction, key);
-      });
+      return PersistencePromise.forEach(
+        removedDocuments,
+        (key: DocumentKey) => {
+          return this.referenceDelegate.removeMutationReference(
+            transaction,
+            key
+          );
+        }
+      );
     });
   }
 
diff --git a/packages/firestore/src/local/indexeddb_persistence.ts b/packages/firestore/src/local/indexeddb_persistence.ts
index 843855df396..aaa87e78059 100644
--- a/packages/firestore/src/local/indexeddb_persistence.ts
+++ b/packages/firestore/src/local/indexeddb_persistence.ts
@@ -116,7 +116,7 @@ const ZOMBIED_CLIENTS_KEY_PREFIX = 'firestore_zombie';
 export class IndexedDbTransaction extends PersistenceTransaction {
   constructor(
     readonly simpleDbTransaction: SimpleDbTransaction,
-    readonly currentSequenceNumber
+    readonly currentSequenceNumber: ListenSequenceNumber
   ) {
     super();
   }
@@ -515,8 +515,10 @@ export class IndexedDbPersistence implements Persistence {
             })
             .next(() =>
               // Delete metadata for clients that are no longer considered active.
-              PersistencePromise.forEach(inactiveClients, inactiveClient =>
-                metadataStore.delete(inactiveClient.clientId)
+              PersistencePromise.forEach(
+                inactiveClients,
+                (inactiveClient: DbClientMetadata) =>
+                  metadataStore.delete(inactiveClient.clientId)
               )
             )
             .next(() => {
@@ -882,7 +884,9 @@ export class IndexedDbPersistence implements Persistence {
    * Obtains or extends the new primary lease for the local client. This
    * method does not verify that the client is eligible for this lease.
    */
-  private acquireOrExtendPrimaryLease(txn): PersistencePromise<void> {
+  private acquireOrExtendPrimaryLease(
+    txn: SimpleDbTransaction
+  ): PersistencePromise<void> {
     const newPrimary = new DbPrimaryClient(
       this.clientId,
       this.allowTabSynchronization,
diff --git a/packages/firestore/src/local/indexeddb_query_cache.ts b/packages/firestore/src/local/indexeddb_query_cache.ts
index 8925f97dac2..06cf1e9852a 100644
--- a/packages/firestore/src/local/indexeddb_query_cache.ts
+++ b/packages/firestore/src/local/indexeddb_query_cache.ts
@@ -293,7 +293,7 @@ export class IndexedDbQueryCache implements QueryCache {
     // PORTING NOTE: The reverse index (documentsTargets) is maintained by
     // IndexedDb.
     const store = documentTargetStore(txn);
-    return PersistencePromise.forEach(keys, key => {
+    return PersistencePromise.forEach(keys, (key: DocumentKey) => {
       const path = EncodedResourcePath.encode(key.path);
       return PersistencePromise.waitFor([
         store.delete([targetId, path]),
diff --git a/packages/firestore/src/local/indexeddb_schema.ts b/packages/firestore/src/local/indexeddb_schema.ts
index c4be56980a4..a6c72de035e 100644
--- a/packages/firestore/src/local/indexeddb_schema.ts
+++ b/packages/firestore/src/local/indexeddb_schema.ts
@@ -162,7 +162,7 @@ export class SchemaConverter implements SimpleDbSchemaConverter {
     );
 
     return queuesStore.loadAll().next(queues => {
-      return PersistencePromise.forEach(queues, queue => {
+      return PersistencePromise.forEach(queues, (queue: DbMutationQueue) => {
         const range = IDBKeyRange.bound(
           [queue.userId, BATCHID_UNKNOWN],
           [queue.userId, queue.lastAcknowledgedBatchId]
@@ -171,17 +171,20 @@ export class SchemaConverter implements SimpleDbSchemaConverter {
         return mutationsStore
           .loadAll(DbMutationBatch.userMutationsIndex, range)
           .next(dbBatches => {
-            return PersistencePromise.forEach(dbBatches, dbBatch => {
-              assert(
-                dbBatch.userId === queue.userId,
-                `Cannot process batch ${dbBatch.batchId} from unexpected user`
-              );
-              const batch = this.serializer.fromDbMutationBatch(dbBatch);
-
-              return removeMutationBatch(txn, queue.userId, batch).next(
-                () => {}
-              );
-            });
+            return PersistencePromise.forEach(
+              dbBatches,
+              (dbBatch: DbMutationBatch) => {
+                assert(
+                  dbBatch.userId === queue.userId,
+                  `Cannot process batch ${dbBatch.batchId} from unexpected user`
+                );
+                const batch = this.serializer.fromDbMutationBatch(dbBatch);
+
+                return removeMutationBatch(txn, queue.userId, batch).next(
+                  () => {}
+                );
+              }
+            );
           });
       });
     });
@@ -246,7 +249,7 @@ export class SchemaConverter implements SimpleDbSchemaConverter {
 
     // Helper to add an index entry iff we haven't already written it.
     const cache = new MemoryCollectionParentIndex();
-    const addEntry = collectionPath => {
+    const addEntry = (collectionPath: ResourcePath) => {
       if (cache.add(collectionPath)) {
         const collectionId = collectionPath.lastSegment();
         const parentPath = collectionPath.popLast();
diff --git a/packages/firestore/src/local/local_documents_view.ts b/packages/firestore/src/local/local_documents_view.ts
index 25510580742..8aa0885451d 100644
--- a/packages/firestore/src/local/local_documents_view.ts
+++ b/packages/firestore/src/local/local_documents_view.ts
@@ -186,7 +186,7 @@ export class LocalDocumentsView {
       .next(parents => {
         // Perform a collection query against each parent that contains the
         // collectionId and aggregate the results.
-        return PersistencePromise.forEach(parents, parent => {
+        return PersistencePromise.forEach(parents, (parent: ResourcePath) => {
           const collectionQuery = query.asCollectionQueryAtPath(
             parent.child(collectionId)
           );
diff --git a/packages/firestore/src/local/local_store.ts b/packages/firestore/src/local/local_store.ts
index b900e622186..dc9b8c2a55b 100644
--- a/packages/firestore/src/local/local_store.ts
+++ b/packages/firestore/src/local/local_store.ts
@@ -651,19 +651,24 @@ export class LocalStore {
       'notifyLocalViewChanges',
       'readwrite',
       txn => {
-        return PersistencePromise.forEach(viewChanges, viewChange => {
-          this.localViewReferences.addReferences(
-            viewChange.addedKeys,
-            viewChange.targetId
-          );
-          this.localViewReferences.removeReferences(
-            viewChange.removedKeys,
-            viewChange.targetId
-          );
-          return PersistencePromise.forEach(viewChange.removedKeys, key =>
-            this.persistence.referenceDelegate.removeReference(txn, key)
-          );
-        });
+        return PersistencePromise.forEach(
+          viewChanges,
+          (viewChange: LocalViewChanges) => {
+            this.localViewReferences.addReferences(
+              viewChange.addedKeys,
+              viewChange.targetId
+            );
+            this.localViewReferences.removeReferences(
+              viewChange.removedKeys,
+              viewChange.targetId
+            );
+            return PersistencePromise.forEach(
+              viewChange.removedKeys,
+              (key: DocumentKey) =>
+                this.persistence.referenceDelegate.removeReference(txn, key)
+            );
+          }
+        );
       }
     );
   }
@@ -772,7 +777,7 @@ export class LocalStore {
           );
           delete this.queryDataByTarget[targetId];
           if (!keepPersistedQueryData) {
-            return PersistencePromise.forEach(removed, key =>
+            return PersistencePromise.forEach(removed, (key: DocumentKey) =>
               this.persistence.referenceDelegate.removeReference(txn, key)
             ).next(() =>
               this.persistence.referenceDelegate.removeTarget(
diff --git a/packages/firestore/src/local/lru_garbage_collector.ts b/packages/firestore/src/local/lru_garbage_collector.ts
index a74ec8a7b1a..1fd748aa77e 100644
--- a/packages/firestore/src/local/lru_garbage_collector.ts
+++ b/packages/firestore/src/local/lru_garbage_collector.ts
@@ -371,7 +371,7 @@ export class LruGarbageCollector {
     activeTargetIds: ActiveTargets
   ): PersistencePromise<LruResults> {
     let upperBoundSequenceNumber: number;
-    let sequenceNumbersToCollect, targetsRemoved: number;
+    let sequenceNumbersToCollect: number, targetsRemoved: number;
     // Timestamps for various pieces of the process
     let startTs: number,
       countedTargetsTs: number,
diff --git a/packages/firestore/src/local/memory_mutation_queue.ts b/packages/firestore/src/local/memory_mutation_queue.ts
index c70ae7bca7b..e384d329371 100644
--- a/packages/firestore/src/local/memory_mutation_queue.ts
+++ b/packages/firestore/src/local/memory_mutation_queue.ts
@@ -303,7 +303,7 @@ export class MemoryMutationQueue implements MutationQueue {
     this.mutationQueue.shift();
 
     let references = this.batchesByDocumentKey;
-    return PersistencePromise.forEach(batch.mutations, mutation => {
+    return PersistencePromise.forEach(batch.mutations, (mutation: Mutation) => {
       const ref = new DocReference(mutation.key, batch.batchId);
       references = references.delete(ref);
       return this.referenceDelegate.removeMutationReference(
diff --git a/packages/firestore/src/local/memory_persistence.ts b/packages/firestore/src/local/memory_persistence.ts
index f61f2ee1c7e..cc8e1f7a86e 100644
--- a/packages/firestore/src/local/memory_persistence.ts
+++ b/packages/firestore/src/local/memory_persistence.ts
@@ -261,17 +261,20 @@ export class MemoryEagerDelegate implements ReferenceDelegate {
     txn: PersistenceTransaction
   ): PersistencePromise<void> {
     const cache = this.persistence.getRemoteDocumentCache();
-    return PersistencePromise.forEach(this.orphanedDocuments, key => {
-      return this.isReferenced(txn, key).next(isReferenced => {
-        if (!isReferenced) {
-          // Since this is the eager delegate and memory persistence,
-          // we don't care about the size of documents. We don't track
-          // the size of the cache for eager GC.
-          return cache.removeEntry(txn, key).next(() => {});
-        }
-        return PersistencePromise.resolve();
-      });
-    });
+    return PersistencePromise.forEach(
+      this.orphanedDocuments,
+      (key: DocumentKey) => {
+        return this.isReferenced(txn, key).next(isReferenced => {
+          if (!isReferenced) {
+            // Since this is the eager delegate and memory persistence,
+            // we don't care about the size of documents. We don't track
+            // the size of the cache for eager GC.
+            return cache.removeEntry(txn, key).next(() => {});
+          }
+          return PersistencePromise.resolve();
+        });
+      }
+    );
   }
 
   updateLimboDocument(
diff --git a/packages/firestore/src/local/memory_remote_document_cache.ts b/packages/firestore/src/local/memory_remote_document_cache.ts
index 99f75aaa6d1..1848c565562 100644
--- a/packages/firestore/src/local/memory_remote_document_cache.ts
+++ b/packages/firestore/src/local/memory_remote_document_cache.ts
@@ -191,7 +191,7 @@ export class MemoryRemoteDocumentCache implements RemoteDocumentCache {
     transaction: PersistenceTransaction,
     f: (key: DocumentKey) => PersistencePromise<void>
   ): PersistencePromise<void> {
-    return PersistencePromise.forEach(this.docs, key => f(key));
+    return PersistencePromise.forEach(this.docs, (key: DocumentKey) => f(key));
   }
 
   getNewDocumentChanges(
diff --git a/packages/firestore/src/local/shared_client_state.ts b/packages/firestore/src/local/shared_client_state.ts
index fbbb19c6da6..c87b01d290f 100644
--- a/packages/firestore/src/local/shared_client_state.ts
+++ b/packages/firestore/src/local/shared_client_state.ts
@@ -462,13 +462,13 @@ export class SharedOnlineState {
 
     const validData =
       typeof onlineState === 'object' &&
-      OnlineState[onlineState.onlineState] !== undefined &&
+      onlineState.onlineState in OnlineState &&
       typeof onlineState.clientId === 'string';
 
     if (validData) {
       return new SharedOnlineState(
         onlineState.clientId,
-        OnlineState[onlineState.onlineState]
+        OnlineState[onlineState.onlineState as keyof typeof OnlineState]
       );
     } else {
       error(LOG_TAG, `Failed to parse online state: ${value}`);
diff --git a/packages/firestore/src/local/simple_db.ts b/packages/firestore/src/local/simple_db.ts
index 9362fcb8da2..b3947a2b02c 100644
--- a/packages/firestore/src/local/simple_db.ts
+++ b/packages/firestore/src/local/simple_db.ts
@@ -579,7 +579,7 @@ export class SimpleDbStore<
       options = {};
       callback = optionsOrCallback as IterateCallback<KeyType, ValueType>;
     } else {
-      options = optionsOrCallback;
+      options = optionsOrCallback as IterateOptions;
     }
     const cursor = this.cursor(options);
     return this.iterateCursor(cursor, callback);
diff --git a/packages/firestore/src/platform_browser/webchannel_connection.ts b/packages/firestore/src/platform_browser/webchannel_connection.ts
index 6326674441a..f264d0a4588 100644
--- a/packages/firestore/src/platform_browser/webchannel_connection.ts
+++ b/packages/firestore/src/platform_browser/webchannel_connection.ts
@@ -20,6 +20,7 @@ import {
   ErrorCode,
   EventType,
   WebChannel,
+  WebChannelOptions,
   XhrIo
 } from '@firebase/webchannel-wrapper';
 
@@ -46,7 +47,7 @@ const RPC_STREAM_SERVICE = 'google.firestore.v1.Firestore';
 const RPC_URL_VERSION = 'v1';
 
 /** Maps RPC names to the corresponding REST endpoint name. */
-const RPC_NAME_REST_MAPPING = {
+const RPC_NAME_REST_MAPPING: { [key: string]: string } = {
   BatchGetDocuments: 'batchGet',
   Commit: 'commit'
 };
@@ -192,7 +193,7 @@ export class WebChannelConnection implements Connection {
       '/channel'
     ];
     const webchannelTransport = createWebChannelTransport();
-    const request = {
+    const request: WebChannelOptions = {
       // Background channel test avoids the initial two test calls and decreases
       // initial cold start time.
       // TODO(dimond): wenboz@ mentioned this might affect use with proxies and
@@ -223,7 +224,7 @@ export class WebChannelConnection implements Connection {
       forceLongPolling: this.forceLongPolling
     };
 
-    this.modifyHeadersForRequest(request.initMessageHeaders, token);
+    this.modifyHeadersForRequest(request.initMessageHeaders!, token);
 
     // Sending the custom headers we just added to request.initMessageHeaders
     // (Authorization, etc.) will trigger the browser to make a CORS preflight
@@ -243,7 +244,7 @@ export class WebChannelConnection implements Connection {
     // ReactNative and so we exclude it, which just means ReactNative may be
     // subject to the extra network roundtrip for CORS preflight.
     if (!isReactNative()) {
-      request['httpHeadersOverwriteParam'] = '$httpHeaders';
+      request.httpHeadersOverwriteParam = '$httpHeaders';
     }
 
     const url = urlParts.join('');
@@ -343,9 +344,10 @@ export class WebChannelConnection implements Connection {
           // (and only errors) to be wrapped in an extra array. To be forward
           // compatible with the bug we need to check either condition. The latter
           // can be removed once the fix has been rolled out.
+          // tslint:disable-next-line:no-any msgData.error is not typed.
+          const msgDataAsAny: any = msgData;
           const error =
-            // tslint:disable-next-line:no-any msgData.error is not typed.
-            (msgData as any).error || (msgData[0] && msgData[0].error);
+            msgDataAsAny.error || (msgDataAsAny[0] && msgDataAsAny[0].error);
           if (error) {
             log.debug(LOG_TAG, 'WebChannel received error:', error);
             // error.status will be a string like 'OK' or 'NOT_FOUND'.
diff --git a/packages/firestore/src/platform_node/grpc_connection.ts b/packages/firestore/src/platform_node/grpc_connection.ts
index 127c985be27..da6b1a7f262 100644
--- a/packages/firestore/src/platform_node/grpc_connection.ts
+++ b/packages/firestore/src/platform_node/grpc_connection.ts
@@ -86,7 +86,8 @@ export class GrpcConnection implements Connection {
   private cachedStub: GeneratedGrpcStub | null = null;
 
   constructor(protos: grpc.GrpcObject, private databaseInfo: DatabaseInfo) {
-    this.firestore = protos['google']['firestore']['v1'];
+    // tslint:disable-next-line:no-any
+    this.firestore = (protos as any)['google']['firestore']['v1'];
   }
 
   private ensureActiveStub(): GeneratedGrpcStub {
diff --git a/packages/firestore/src/util/input_validation.ts b/packages/firestore/src/util/input_validation.ts
index b37b109db2a..339c70883f7 100644
--- a/packages/firestore/src/util/input_validation.ts
+++ b/packages/firestore/src/util/input_validation.ts
@@ -202,7 +202,7 @@ export function validateArrayElements<T>(
   optionName: string,
   typeDescription: string,
   argument: T[],
-  validator: (T) => boolean
+  validator: (arg0: T) => boolean
 ): void {
   if (!(argument instanceof Array)) {
     throw new FirestoreError(
@@ -229,7 +229,7 @@ export function validateOptionalArrayElements<T>(
   optionName: string,
   typeDescription: string,
   argument: T[] | undefined,
-  validator: (T) => boolean
+  validator: (arg0: T) => boolean
 ): void {
   if (argument !== undefined) {
     validateArrayElements(
diff --git a/packages/firestore/src/util/misc.ts b/packages/firestore/src/util/misc.ts
index 026c5bc34da..ca2750757bb 100644
--- a/packages/firestore/src/util/misc.ts
+++ b/packages/firestore/src/util/misc.ts
@@ -18,6 +18,7 @@
 import { assert } from './assert';
 
 export type EventHandler<E> = (value: E) => void;
+export type Indexable = { [k: string]: unknown };
 
 // tslint:disable-next-line:class-as-namespace
 export class AutoId {
diff --git a/packages/firestore/test/integration/api/array_transforms.test.ts b/packages/firestore/test/integration/api/array_transforms.test.ts
index 2b2deaf81cc..ab5eb4c513d 100644
--- a/packages/firestore/test/integration/api/array_transforms.test.ts
+++ b/packages/firestore/test/integration/api/array_transforms.test.ts
@@ -31,7 +31,7 @@ const FieldValue = firebase.firestore!.FieldValue;
  * together, etc.) and so these tests mostly focus on the array transform
  * semantics.
  */
-apiDescribe('Array Transforms:', persistence => {
+apiDescribe('Array Transforms:', (persistence: boolean) => {
   // A document reference to read and write to.
   let docRef: firestore.DocumentReference;
 
diff --git a/packages/firestore/test/integration/api/batch_writes.test.ts b/packages/firestore/test/integration/api/batch_writes.test.ts
index 0c020f642a4..88e21abff5e 100644
--- a/packages/firestore/test/integration/api/batch_writes.test.ts
+++ b/packages/firestore/test/integration/api/batch_writes.test.ts
@@ -26,7 +26,7 @@ const apiDescribe = integrationHelpers.apiDescribe;
 const Timestamp = firebase.firestore!.Timestamp;
 const FieldValue = firebase.firestore!.FieldValue;
 
-apiDescribe('Database batch writes', persistence => {
+apiDescribe('Database batch writes', (persistence: boolean) => {
   it('supports empty batches', () => {
     return integrationHelpers.withTestDb(persistence, db => {
       return db.batch().commit();
diff --git a/packages/firestore/test/integration/api/cursor.test.ts b/packages/firestore/test/integration/api/cursor.test.ts
index c4d2da1094f..bdc975997ba 100644
--- a/packages/firestore/test/integration/api/cursor.test.ts
+++ b/packages/firestore/test/integration/api/cursor.test.ts
@@ -30,7 +30,7 @@ import {
 const Timestamp = firebase.firestore!.Timestamp;
 const FieldPath = firebase.firestore!.FieldPath;
 
-apiDescribe('Cursors', persistence => {
+apiDescribe('Cursors', (persistence: boolean) => {
   it('can page through items', () => {
     const testDocs = {
       a: { v: 'a' },
@@ -242,7 +242,7 @@ apiDescribe('Cursors', persistence => {
 
   // Currently, timestamps are truncated to microseconds on the backend, so
   // don't create timestamps with more precision than that.
-  const makeTimestamp = (seconds, micros) =>
+  const makeTimestamp = (seconds: number, micros: number) =>
     new Timestamp(seconds, micros * 1000);
 
   it('can accept Timestamps as bounds', () => {
diff --git a/packages/firestore/test/integration/api/database.test.ts b/packages/firestore/test/integration/api/database.test.ts
index 090215b872d..a33b1af0120 100644
--- a/packages/firestore/test/integration/api/database.test.ts
+++ b/packages/firestore/test/integration/api/database.test.ts
@@ -44,7 +44,7 @@ chai.use(chaiAsPromised);
 const Timestamp = firebase.firestore!.Timestamp;
 const FieldValue = firebase.firestore!.FieldValue;
 
-apiDescribe('Database', persistence => {
+apiDescribe('Database', (persistence: boolean) => {
   it('can set a document', () => {
     return withTestDoc(persistence, docRef => {
       return docRef.set({
@@ -536,7 +536,7 @@ apiDescribe('Database', persistence => {
     });
   });
 
-  apiDescribe('Queries are validated client-side', persistence => {
+  apiDescribe('Queries are validated client-side', (persistence: boolean) => {
     // NOTE: Failure cases are validated in validation_test.ts
 
     it('same inequality fields works', () => {
diff --git a/packages/firestore/test/integration/api/fields.test.ts b/packages/firestore/test/integration/api/fields.test.ts
index cfb41183f5b..e489761e0ba 100644
--- a/packages/firestore/test/integration/api/fields.test.ts
+++ b/packages/firestore/test/integration/api/fields.test.ts
@@ -35,7 +35,7 @@ const Timestamp = firebase.firestore!.Timestamp;
 // tslint:disable-next-line:no-any Allow custom types for testing.
 type AnyTestData = any;
 
-apiDescribe('Nested Fields', persistence => {
+apiDescribe('Nested Fields', (persistence: boolean) => {
   const testData = (n?: number): AnyTestData => {
     n = n || 1;
     return {
@@ -240,7 +240,7 @@ apiDescribe('Nested Fields', persistence => {
 // NOTE(mikelehen): I originally combined these tests with the above ones, but
 // Datastore currently prohibits having nested fields and fields with dots in
 // the same entity, so I'm separating them.
-apiDescribe('Fields with special characters', persistence => {
+apiDescribe('Fields with special characters', (persistence: boolean) => {
   const testData = (n?: number): AnyTestData => {
     n = n || 1;
     return {
@@ -346,7 +346,7 @@ apiDescribe('Fields with special characters', persistence => {
   });
 });
 
-apiDescribe('Timestamp Fields in snapshots', persistence => {
+apiDescribe('Timestamp Fields in snapshots', (persistence: boolean) => {
   // tslint:disable-next-line:no-any Figure out how to pass in the Timestamp type
   const testDataWithTimestamps = (ts: any): AnyTestData => {
     return { timestamp: ts, nested: { timestamp2: ts } };
diff --git a/packages/firestore/test/integration/api/get_options.test.ts b/packages/firestore/test/integration/api/get_options.test.ts
index 1d693f06f88..78b349a4f8e 100644
--- a/packages/firestore/test/integration/api/get_options.test.ts
+++ b/packages/firestore/test/integration/api/get_options.test.ts
@@ -23,7 +23,7 @@ import {
   withTestDocAndInitialData
 } from '../util/helpers';
 
-apiDescribe('GetOptions', persistence => {
+apiDescribe('GetOptions', (persistence: boolean) => {
   it('get document while online with default get options', () => {
     const initialData = { key: 'value' };
     return withTestDocAndInitialData(persistence, initialData, docRef => {
diff --git a/packages/firestore/test/integration/api/numeric_transforms.test.ts b/packages/firestore/test/integration/api/numeric_transforms.test.ts
index a498d67ab80..dc522ac8287 100644
--- a/packages/firestore/test/integration/api/numeric_transforms.test.ts
+++ b/packages/firestore/test/integration/api/numeric_transforms.test.ts
@@ -27,7 +27,7 @@ const FieldValue = firebase.firestore!.FieldValue;
 
 const DOUBLE_EPSILON = 0.000001;
 
-apiDescribe('Numeric Transforms:', persistence => {
+apiDescribe('Numeric Transforms:', (persistence: boolean) => {
   // A document reference to read and write to.
   let docRef: firestore.DocumentReference;
 
diff --git a/packages/firestore/test/integration/api/query.test.ts b/packages/firestore/test/integration/api/query.test.ts
index 725607a938c..fc107288f74 100644
--- a/packages/firestore/test/integration/api/query.test.ts
+++ b/packages/firestore/test/integration/api/query.test.ts
@@ -40,7 +40,7 @@ const FieldPath = firebase.firestore!.FieldPath;
 const GeoPoint = firebase.firestore!.GeoPoint;
 const Timestamp = firebase.firestore!.Timestamp;
 
-apiDescribe('Queries', persistence => {
+apiDescribe('Queries', (persistence: boolean) => {
   addEqualityMatcher();
 
   it('can issue limit queries', () => {
diff --git a/packages/firestore/test/integration/api/server_timestamp.test.ts b/packages/firestore/test/integration/api/server_timestamp.test.ts
index 574ee170d0a..76f44a1a89d 100644
--- a/packages/firestore/test/integration/api/server_timestamp.test.ts
+++ b/packages/firestore/test/integration/api/server_timestamp.test.ts
@@ -28,7 +28,7 @@ type AnyTestData = any;
 const Timestamp = firebase.firestore!.Timestamp;
 const FieldValue = firebase.firestore!.FieldValue;
 
-apiDescribe('Server Timestamps', persistence => {
+apiDescribe('Server Timestamps', (persistence: boolean) => {
   // Data written in tests via set().
   const setData = {
     a: 42,
diff --git a/packages/firestore/test/integration/api/smoke.test.ts b/packages/firestore/test/integration/api/smoke.test.ts
index dc88f621117..14c19fc660b 100644
--- a/packages/firestore/test/integration/api/smoke.test.ts
+++ b/packages/firestore/test/integration/api/smoke.test.ts
@@ -22,7 +22,7 @@ import * as integrationHelpers from '../util/helpers';
 
 const apiDescribe = integrationHelpers.apiDescribe;
 
-apiDescribe('Smoke Test', persistence => {
+apiDescribe('Smoke Test', (persistence: boolean) => {
   it('can write a single document', () => {
     return integrationHelpers.withTestDoc(persistence, ref => {
       return ref.set({
diff --git a/packages/firestore/test/integration/api/transactions.test.ts b/packages/firestore/test/integration/api/transactions.test.ts
index 0175251b58e..074d1e84cfc 100644
--- a/packages/firestore/test/integration/api/transactions.test.ts
+++ b/packages/firestore/test/integration/api/transactions.test.ts
@@ -23,7 +23,7 @@ import * as integrationHelpers from '../util/helpers';
 
 const apiDescribe = integrationHelpers.apiDescribe;
 
-apiDescribe('Database transactions', persistence => {
+apiDescribe('Database transactions', (persistence: boolean) => {
   // TODO(klimt): Test that transactions don't see latency compensation
   // changes, using the other kind of integration test.
   // We currently require every document read to also be written.
diff --git a/packages/firestore/test/integration/api/type.test.ts b/packages/firestore/test/integration/api/type.test.ts
index 5539e753d9b..8a870baade9 100644
--- a/packages/firestore/test/integration/api/type.test.ts
+++ b/packages/firestore/test/integration/api/type.test.ts
@@ -21,7 +21,7 @@ import { addEqualityMatcher } from '../../util/equality_matcher';
 import firebase from '../util/firebase_export';
 import { apiDescribe, withTestDb, withTestDoc } from '../util/helpers';
 
-apiDescribe('Firestore', persistence => {
+apiDescribe('Firestore', (persistence: boolean) => {
   addEqualityMatcher();
 
   function expectRoundtrip(
diff --git a/packages/firestore/test/integration/api/validation.test.ts b/packages/firestore/test/integration/api/validation.test.ts
index 6b7d6b1e333..c1e10645f87 100644
--- a/packages/firestore/test/integration/api/validation.test.ts
+++ b/packages/firestore/test/integration/api/validation.test.ts
@@ -109,7 +109,7 @@ class TestClass {
 // since it is an untyped language. These tests are not exhaustive as that would
 // be extremely tedious, but we do try to hit every error template at least
 // once.
-apiDescribe('Validation:', persistence => {
+apiDescribe('Validation:', (persistence: boolean) => {
   describe('FirestoreSettings', () => {
     // Enabling persistence counts as a use of the firestore instance, meaning
     // that it will be impossible to verify that a set of settings don't throw,
diff --git a/packages/firestore/test/integration/api_internal/idle_timeout.test.ts b/packages/firestore/test/integration/api_internal/idle_timeout.test.ts
index c19f3f3ab58..f13df17db04 100644
--- a/packages/firestore/test/integration/api_internal/idle_timeout.test.ts
+++ b/packages/firestore/test/integration/api_internal/idle_timeout.test.ts
@@ -20,7 +20,7 @@ import { Deferred } from '../../util/promise';
 import { apiDescribe, withTestDb } from '../util/helpers';
 import { asyncQueue } from '../util/internal_helpers';
 
-apiDescribe('Idle Timeout', persistence => {
+apiDescribe('Idle Timeout', (persistence: boolean) => {
   it('can write document after idle timeout', () => {
     return withTestDb(persistence, db => {
       const docRef = db.collection('test-collection').doc();
diff --git a/packages/firestore/test/integration/util/helpers.ts b/packages/firestore/test/integration/util/helpers.ts
index 80528a7c410..429abcffb0b 100644
--- a/packages/firestore/test/integration/util/helpers.ts
+++ b/packages/firestore/test/integration/util/helpers.ts
@@ -128,7 +128,7 @@ export function toChangesArray(
 export function toDataMap(
   docSet: firestore.QuerySnapshot
 ): { [field: string]: firestore.DocumentData } {
-  const docsData = {};
+  const docsData: { [field: string]: firestore.DocumentData } = {};
   docSet.forEach(doc => {
     docsData[doc.id] = doc.data();
   });
diff --git a/packages/firestore/test/unit/local/indexeddb_persistence.test.ts b/packages/firestore/test/unit/local/indexeddb_persistence.test.ts
index c331eb9f00c..2e5a73edbc7 100644
--- a/packages/firestore/test/unit/local/indexeddb_persistence.test.ts
+++ b/packages/firestore/test/unit/local/indexeddb_persistence.test.ts
@@ -54,6 +54,7 @@ import { PersistencePromise } from '../../../src/local/persistence_promise';
 import { ClientId } from '../../../src/local/shared_client_state';
 import { SimpleDb, SimpleDbTransaction } from '../../../src/local/simple_db';
 import { PlatformSupport } from '../../../src/platform/platform';
+import { firestoreV1ApiClientInterfaces } from '../../../src/protos/firestore_proto_api';
 import { JsonProtoSerializer } from '../../../src/remote/serializer';
 import { AsyncQueue } from '../../../src/util/async_queue';
 import { FirestoreError } from '../../../src/util/error';
@@ -68,7 +69,7 @@ import {
 } from './persistence_test_helpers';
 
 function withDb(
-  schemaVersion,
+  schemaVersion: number,
   fn: (db: IDBDatabase) => Promise<void>
 ): Promise<void> {
   const schemaConverter = new SchemaConverter(TEST_SERIALIZER);
@@ -310,8 +311,9 @@ describe('IndexedDbSchema: createOrUpgradeDb', () => {
       const sdb = new SimpleDb(db);
       return sdb.runTransaction('readwrite', [DbMutationBatch.store], txn => {
         const store = txn.store(DbMutationBatch.store);
-        return PersistencePromise.forEach(testMutations, testMutation =>
-          store.put(testMutation)
+        return PersistencePromise.forEach(
+          testMutations,
+          (testMutation: DbMutationBatch) => store.put(testMutation)
         );
       });
     }).then(() =>
@@ -324,10 +326,12 @@ describe('IndexedDbSchema: createOrUpgradeDb', () => {
           const store = txn.store<DbMutationBatchKey, DbMutationBatch>(
             DbMutationBatch.store
           );
-          let p = PersistencePromise.forEach(testMutations, testMutation =>
-            store.get(testMutation.batchId).next(mutationBatch => {
-              expect(mutationBatch).to.deep.equal(testMutation);
-            })
+          let p = PersistencePromise.forEach(
+            testMutations,
+            (testMutation: DbMutationBatch) =>
+              store.get(testMutation.batchId).next(mutationBatch => {
+                expect(mutationBatch).to.deep.equal(testMutation);
+              })
           );
           p = p.next(() => {
             store
@@ -424,21 +428,27 @@ describe('IndexedDbSchema: createOrUpgradeDb', () => {
           DbMutationQueue
         >(DbMutationQueue.store);
         // Manually populate the mutation queue and create all indicies.
-        return PersistencePromise.forEach(testMutations, testMutation => {
-          return mutationBatchStore.put(testMutation).next(() => {
-            return PersistencePromise.forEach(testMutation.mutations, write => {
-              const indexKey = DbDocumentMutation.key(
-                testMutation.userId,
-                path(write.update!.name!, 5),
-                testMutation.batchId
-              );
-              return documentMutationStore.put(
-                indexKey,
-                DbDocumentMutation.PLACEHOLDER
+        return PersistencePromise.forEach(
+          testMutations,
+          (testMutation: DbMutationBatch) => {
+            return mutationBatchStore.put(testMutation).next(() => {
+              return PersistencePromise.forEach(
+                testMutation.mutations,
+                (write: firestoreV1ApiClientInterfaces.Write) => {
+                  const indexKey = DbDocumentMutation.key(
+                    testMutation.userId,
+                    path(write.update!.name!, 5),
+                    testMutation.batchId
+                  );
+                  return documentMutationStore.put(
+                    indexKey,
+                    DbDocumentMutation.PLACEHOLDER
+                  );
+                }
               );
             });
-          });
-        }).next(() =>
+          }
+        ).next(() =>
           // Populate the mutation queues' metadata
           PersistencePromise.waitFor([
             mutationQueuesStore.put(new DbMutationQueue('foo', 2, '')),
@@ -509,8 +519,10 @@ describe('IndexedDbSchema: createOrUpgradeDb', () => {
         const store = txn.store<DbRemoteDocumentKey, DbRemoteDocument>(
           DbRemoteDocument.store
         );
-        return PersistencePromise.forEach(dbRemoteDocs, ({ dbKey, dbDoc }) =>
-          store.put(dbKey, dbDoc)
+        return PersistencePromise.forEach(
+          dbRemoteDocs,
+          ({ dbKey, dbDoc }: { dbKey: string[]; dbDoc: DbRemoteDocument }) =>
+            store.put(dbKey, dbDoc)
         );
       });
     });
@@ -652,7 +664,7 @@ describe('IndexedDbSchema: createOrUpgradeDb', () => {
         >(DbDocumentMutation.store);
         // We "cheat" and only write the DbDocumentMutation index entries, since that's
         // all the migration uses.
-        return PersistencePromise.forEach(writePaths, writePath => {
+        return PersistencePromise.forEach(writePaths, (writePath: string) => {
           const indexKey = DbDocumentMutation.key(
             'dummy-uid',
             path(writePath),
@@ -664,7 +676,7 @@ describe('IndexedDbSchema: createOrUpgradeDb', () => {
           );
         }).next(() => {
           // Write the remote document entries.
-          return PersistencePromise.forEach(remoteDocPaths, path => {
+          return PersistencePromise.forEach(remoteDocPaths, (path: string) => {
             const remoteDoc = doc(path, /*version=*/ 1, { data: 1 });
             return remoteDocumentStore.put(
               remoteDoc.key.path.toArray(),
@@ -684,7 +696,7 @@ describe('IndexedDbSchema: createOrUpgradeDb', () => {
           DbCollectionParent
         >(DbCollectionParent.store);
         return collectionParentsStore.loadAll().next(indexEntries => {
-          const actualParents = {};
+          const actualParents: { [key: string]: string[] } = {};
           for (const { collectionId, parent } of indexEntries) {
             let parents = actualParents[collectionId];
             if (!parents) {
diff --git a/packages/firestore/test/unit/local/local_store.test.ts b/packages/firestore/test/unit/local/local_store.test.ts
index 5f1076ab656..97a0009fed1 100644
--- a/packages/firestore/test/unit/local/local_store.test.ts
+++ b/packages/firestore/test/unit/local/local_store.test.ts
@@ -76,7 +76,7 @@ class LocalStoreTester {
   private lastChanges: MaybeDocumentMap | null = null;
   private lastTargetId: TargetId | null = null;
   private batches: MutationBatch[] = [];
-  constructor(public localStore: LocalStore, readonly gcIsEager) {}
+  constructor(public localStore: LocalStore, readonly gcIsEager: boolean) {}
 
   after(
     op: Mutation | Mutation[] | RemoteEvent | LocalViewChanges
diff --git a/packages/firestore/test/unit/local/persistence_promise.test.ts b/packages/firestore/test/unit/local/persistence_promise.test.ts
index 848f962c84c..abb55b84af7 100644
--- a/packages/firestore/test/unit/local/persistence_promise.test.ts
+++ b/packages/firestore/test/unit/local/persistence_promise.test.ts
@@ -232,7 +232,7 @@ describe('PersistencePromise', () => {
   });
 
   it('propagates error for forEach()', () => {
-    const p = PersistencePromise.forEach([true, false], success => {
+    const p = PersistencePromise.forEach([true, false], (success: boolean) => {
       if (success) {
         return PersistencePromise.resolve();
       } else {
diff --git a/packages/firestore/test/unit/local/remote_document_cache.test.ts b/packages/firestore/test/unit/local/remote_document_cache.test.ts
index 3f2ec690fad..134a016d21b 100644
--- a/packages/firestore/test/unit/local/remote_document_cache.test.ts
+++ b/packages/firestore/test/unit/local/remote_document_cache.test.ts
@@ -111,7 +111,7 @@ describe('IndexedDbRemoteDocumentCache', () => {
     docs: MaybeDocument[]
   ): PersistencePromise<void> {
     const changeBuffer = cache.newChangeBuffer();
-    return PersistencePromise.forEach(docs, doc =>
+    return PersistencePromise.forEach(docs, (doc: MaybeDocument) =>
       changeBuffer.getEntry(txn, doc.key).next(() => {})
     ).next(() => {
       for (const doc of docs) {
diff --git a/packages/firestore/test/unit/local/test_remote_document_cache.ts b/packages/firestore/test/unit/local/test_remote_document_cache.ts
index 079c77793b6..2fd0814c165 100644
--- a/packages/firestore/test/unit/local/test_remote_document_cache.ts
+++ b/packages/firestore/test/unit/local/test_remote_document_cache.ts
@@ -56,8 +56,10 @@ export abstract class TestRemoteDocumentCache {
       'readwrite-primary',
       txn => {
         const changeBuffer = this.cache.newChangeBuffer();
-        return PersistencePromise.forEach(maybeDocuments, maybeDocument =>
-          changeBuffer.getEntry(txn, maybeDocument.key).next(() => {})
+        return PersistencePromise.forEach(
+          maybeDocuments,
+          (maybeDocument: MaybeDocument) =>
+            changeBuffer.getEntry(txn, maybeDocument.key).next(() => {})
         ).next(() => {
           for (const maybeDocument of maybeDocuments) {
             changeBuffer.addEntry(maybeDocument);
diff --git a/packages/firestore/test/unit/local/web_storage_shared_client_state.test.ts b/packages/firestore/test/unit/local/web_storage_shared_client_state.test.ts
index 5129b7002e2..e4a15d8f9d4 100644
--- a/packages/firestore/test/unit/local/web_storage_shared_client_state.test.ts
+++ b/packages/firestore/test/unit/local/web_storage_shared_client_state.test.ts
@@ -165,15 +165,25 @@ describe('WebStorageSharedClientState', () => {
   const webStorage = window.localStorage;
 
   let queue: AsyncQueue;
-  let primaryClientId;
+  let primaryClientId: string;
   let sharedClientState: SharedClientState;
   let clientSyncer: TestSharedClientSyncer;
 
-  let previousAddEventListener;
-  let previousRemoveEventListener;
+  let previousAddEventListener: typeof window.addEventListener;
+  let previousRemoveEventListener: typeof window.removeEventListener;
 
-  // tslint:disable-next-line:no-any
-  let webStorageCallbacks: Array<(this, event) => any> = [];
+  interface WebStorageOptions {
+    key: string;
+    storageArea: Storage;
+    newValue: string | null;
+  }
+
+  type WebStorageCallback = (
+    this: unknown,
+    event: WebStorageOptions
+  ) => unknown;
+
+  let webStorageCallbacks: WebStorageCallback[] = [];
 
   function writeToWebStorage(key: string, value: string | null): void {
     for (const callback of webStorageCallbacks) {
@@ -195,9 +205,9 @@ describe('WebStorageSharedClientState', () => {
     // We capture the listener here so that we can invoke it from the local
     // client. If we directly relied on WebStorage listeners, we would not
     // receive events for local writes.
-    window.addEventListener = (type, callback) => {
+    window.addEventListener = (type: string, callback: unknown) => {
       if (type === 'storage') {
-        webStorageCallbacks.push(callback);
+        webStorageCallbacks.push(callback as WebStorageCallback);
       }
     };
     window.removeEventListener = () => {};
diff --git a/packages/firestore/test/unit/remote/node/serializer.test.ts b/packages/firestore/test/unit/remote/node/serializer.test.ts
index 7f2860e970e..5f8f5eea681 100644
--- a/packages/firestore/test/unit/remote/node/serializer.test.ts
+++ b/packages/firestore/test/unit/remote/node/serializer.test.ts
@@ -54,6 +54,7 @@ import {
   WatchTargetChangeState
 } from '../../../../src/remote/watch_change';
 import { Code, FirestoreError } from '../../../../src/util/error';
+import { Indexable } from '../../../../src/util/misc';
 import * as obj from '../../../../src/util/obj';
 import * as types from '../../../../src/util/types';
 import { addEqualityMatcher } from '../../../util/equality_matcher';
@@ -156,7 +157,9 @@ describe('Serializer', () => {
         const actualProtobufjsProto: ProtobufJS.Message = ValueMessage.fromObject(
           actualJsonProto
         );
-        expect(actualProtobufjsProto[valueType]).to.deep.equal(protobufJsValue);
+        expect((actualProtobufjsProto as Indexable)[valueType]).to.deep.equal(
+          protobufJsValue
+        );
 
         // Convert protobufjs back to JSON.
         const returnJsonProto = ValueMessage.toObject(
diff --git a/packages/firestore/test/unit/specs/describe_spec.ts b/packages/firestore/test/unit/specs/describe_spec.ts
index 11bc8bea8c2..1953ed73d48 100644
--- a/packages/firestore/test/unit/specs/describe_spec.ts
+++ b/packages/firestore/test/unit/specs/describe_spec.ts
@@ -83,8 +83,8 @@ export function setSpecJSONHandler(writer: (json: string) => void): void {
 
 /** Gets the test runner based on the specified tags. */
 function getTestRunner(
-  tags,
-  persistenceEnabled
+  tags: string[],
+  persistenceEnabled: boolean
 ): ExclusiveTestFunction | PendingTestFunction {
   if (tags.indexOf(NO_WEB_TAG) >= 0) {
     return it.skip;
@@ -109,7 +109,7 @@ function getTestRunner(
 }
 
 /** If required, returns a custom test timeout for long-running tests */
-function getTestTimeout(tags): number | undefined {
+function getTestTimeout(tags: string[]): number | undefined {
   if (tags.indexOf(BENCHMARK_TAG) >= 0) {
     return BENCHMARK_TEST_TIMEOUT_MS;
   } else {
diff --git a/packages/firestore/test/unit/specs/listen_spec.test.ts b/packages/firestore/test/unit/specs/listen_spec.test.ts
index be1c7d107a3..d706ba00867 100644
--- a/packages/firestore/test/unit/specs/listen_spec.test.ts
+++ b/packages/firestore/test/unit/specs/listen_spec.test.ts
@@ -448,7 +448,7 @@ describeSpec('Listens:', [], () => {
   });
 
   specTest('Listens are reestablished after network disconnect', [], () => {
-    const expectRequestCount = requestCounts =>
+    const expectRequestCount = (requestCounts: { [type: string]: number }) =>
       requestCounts.addTarget + requestCounts.removeTarget;
 
     const query = Query.atPath(path('collection'));
diff --git a/packages/firestore/test/unit/specs/spec_test_runner.ts b/packages/firestore/test/unit/specs/spec_test_runner.ts
index 1ad5574a338..c84c28d7f25 100644
--- a/packages/firestore/test/unit/specs/spec_test_runner.ts
+++ b/packages/firestore/test/unit/specs/spec_test_runner.ts
@@ -1247,7 +1247,7 @@ export async function runSpec(
   const runners: TestRunner[] = [];
   const outstandingMutations = new SharedWriteTracker();
 
-  const ensureRunner = async clientIndex => {
+  const ensureRunner = async (clientIndex: number) => {
     if (!runners[clientIndex]) {
       const platform = new TestPlatform(
         PlatformSupport.getPlatform(),
diff --git a/packages/firestore/test/unit/specs/write_spec.test.ts b/packages/firestore/test/unit/specs/write_spec.test.ts
index 814a4b21251..25b795dfd07 100644
--- a/packages/firestore/test/unit/specs/write_spec.test.ts
+++ b/packages/firestore/test/unit/specs/write_spec.test.ts
@@ -772,7 +772,7 @@ describeSpec('Writes:', [], () => {
   );
 
   specTest('Writes are resent after network disconnect', [], () => {
-    const expectRequestCount = requestCounts =>
+    const expectRequestCount = (requestCounts: { [type: string]: number }) =>
       requestCounts.handshakes + requestCounts.writes + requestCounts.closes;
 
     return spec()
diff --git a/packages/firestore/test/util/equality_matcher.ts b/packages/firestore/test/util/equality_matcher.ts
index 78330b40b1f..d59f4ae175e 100644
--- a/packages/firestore/test/util/equality_matcher.ts
+++ b/packages/firestore/test/util/equality_matcher.ts
@@ -16,6 +16,7 @@
  */
 
 import { use } from 'chai';
+import { Equatable } from '../../src/util/misc';
 
 /**
  * @file This file provides a helper function to add a matcher that matches
@@ -24,12 +25,16 @@ import { use } from 'chai';
  * implementation is used.
  */
 
-function customDeepEqual(left, right): boolean {
+function customDeepEqual(left: unknown, right: unknown): boolean {
   /**
    * START: Custom compare logic
    */
-  if (left && typeof left.isEqual === 'function') return left.isEqual(right);
-  if (right && typeof right.isEqual === 'function') return right.isEqual(left);
+  if (typeof left === 'object' && left && 'isEqual' in left) {
+    return (left as Equatable<unknown>).isEqual(right);
+  }
+  if (typeof right === 'object' && right && 'isEqual' in right) {
+    return (right as Equatable<unknown>).isEqual(left);
+  }
   /**
    * END: Custom compare logic
    */
@@ -44,18 +49,21 @@ function customDeepEqual(left, right): boolean {
   }
   if (typeof left !== typeof right) return false; // needed for structurally different objects
   if (Object(left) !== left) return false; // primitive values
+  // @ts-ignore
   const keys = Object.keys(left);
+  // @ts-ignore
   if (keys.length !== Object.keys(right).length) return false;
   for (let i = 0; i < keys.length; i++) {
     const key = keys[i];
     if (!Object.prototype.hasOwnProperty.call(right, key)) return false;
+    // @ts-ignore
     if (!customDeepEqual(left[key], right[key])) return false;
   }
   return true;
 }
 
 /** The original equality function passed in by chai(). */
-let originalFunction: ((r, l) => boolean) | null = null;
+let originalFunction: ((r: unknown, l: unknown) => boolean) | null = null;
 
 export function addEqualityMatcher(): void {
   let isActive = true;
@@ -64,9 +72,9 @@ export function addEqualityMatcher(): void {
     use((chai, utils) => {
       const Assertion = chai.Assertion;
 
-      const assertEql = _super => {
+      const assertEql = (_super: (r: unknown, l: unknown) => boolean) => {
         originalFunction = originalFunction || _super;
-        return function(...args): void {
+        return function(...args: unknown[]): void {
           if (isActive) {
             const [expected, msg] = args;
             utils.flag(this, 'message', msg);
diff --git a/packages/functions/index.node.ts b/packages/functions/index.node.ts
index 797ed192b76..a0117152ea7 100644
--- a/packages/functions/index.node.ts
+++ b/packages/functions/index.node.ts
@@ -16,7 +16,10 @@
  */
 import firebase from '@firebase/app';
 import { FirebaseApp } from '@firebase/app-types';
-import { FirebaseServiceFactory } from '@firebase/app-types/private';
+import {
+  FirebaseServiceFactory,
+  _FirebaseNamespace
+} from '@firebase/app-types/private';
 import { Service } from './src/api/service';
 import 'isomorphic-fetch';
 
@@ -29,7 +32,7 @@ function factory(app: FirebaseApp, _unused: unknown, region?: string): Service {
   return new Service(app, region);
 }
 
-export function registerFunctions(instance): void {
+export function registerFunctions(instance: _FirebaseNamespace): void {
   const namespaceExports = {
     // no-inline
     Functions: Service
@@ -45,4 +48,4 @@ export function registerFunctions(instance): void {
   );
 }
 
-registerFunctions(firebase);
+registerFunctions(firebase as _FirebaseNamespace);
diff --git a/packages/functions/index.ts b/packages/functions/index.ts
index 508f4b973a0..a8a43581df7 100644
--- a/packages/functions/index.ts
+++ b/packages/functions/index.ts
@@ -16,7 +16,10 @@
  */
 import firebase from '@firebase/app';
 import * as appTypes from '@firebase/app-types';
-import { FirebaseServiceFactory } from '@firebase/app-types/private';
+import {
+  FirebaseServiceFactory,
+  _FirebaseNamespace
+} from '@firebase/app-types/private';
 import * as types from '@firebase/functions-types';
 import { Service } from './src/api/service';
 
@@ -33,7 +36,7 @@ function factory(
   return new Service(app, region);
 }
 
-export function registerFunctions(instance): void {
+export function registerFunctions(instance: _FirebaseNamespace): void {
   const namespaceExports = {
     // no-inline
     Functions: Service
@@ -49,7 +52,7 @@ export function registerFunctions(instance): void {
   );
 }
 
-registerFunctions(firebase);
+registerFunctions(firebase as _FirebaseNamespace);
 
 declare module '@firebase/app-types' {
   interface FirebaseNamespace {
diff --git a/packages/functions/src/serializer.ts b/packages/functions/src/serializer.ts
index b349b34d3f7..68e0ee9cb98 100644
--- a/packages/functions/src/serializer.ts
+++ b/packages/functions/src/serializer.ts
@@ -18,8 +18,11 @@
 const LONG_TYPE = 'type.googleapis.com/google.protobuf.Int64Value';
 const UNSIGNED_LONG_TYPE = 'type.googleapis.com/google.protobuf.UInt64Value';
 
-function mapValues(o: object, f: (val: unknown) => unknown): object {
-  const result = {};
+function mapValues(
+  o: { [key: string]: unknown },
+  f: (arg0: unknown) => unknown
+): object {
+  const result: { [key: string]: unknown } = {};
   for (const key in o) {
     if (o.hasOwnProperty(key)) {
       result[key] = f(o[key]);
@@ -61,19 +64,19 @@ export class Serializer {
 
   // Takes data that's been encoded in a JSON-friendly form and returns a form
   // with richer datatypes, such as Dates, etc.
-  decode(json: {} | null): {} | null {
+  decode(json: unknown): unknown {
     if (json == null) {
       return json;
     }
-    if (json['@type']) {
-      switch (json['@type']) {
+    if ((json as { [key: string]: unknown })['@type']) {
+      switch ((json as { [key: string]: unknown })['@type']) {
         case LONG_TYPE:
         // Fall through and handle this the same as unsigned.
         case UNSIGNED_LONG_TYPE: {
           // Technically, this could work return a valid number for malformed
           // data if there was a number followed by garbage. But it's just not
           // worth all the extra code to detect that case.
-          const value = Number(json['value']);
+          const value = Number((json as { [key: string]: unknown })['value']);
           if (isNaN(value)) {
             throw new Error('Data cannot be decoded from JSON: ' + json);
           }
@@ -88,7 +91,9 @@ export class Serializer {
       return json.map(x => this.decode(x));
     }
     if (typeof json === 'function' || typeof json === 'object') {
-      return mapValues(json, x => this.decode(x as {} | null));
+      return mapValues(json as Function | object, x =>
+        this.decode(x as {} | null)
+      );
     }
     // Anything else is safe to return.
     return json;
diff --git a/packages/logger/src/logger.ts b/packages/logger/src/logger.ts
index eacd8412386..c32d35a2e47 100644
--- a/packages/logger/src/logger.ts
+++ b/packages/logger/src/logger.ts
@@ -141,19 +141,19 @@ export class Logger {
    * The functions below are all based on the `console` interface
    */
 
-  debug(...args): void {
+  debug(...args: unknown[]): void {
     this._logHandler(this, LogLevel.DEBUG, ...args);
   }
-  log(...args): void {
+  log(...args: unknown[]): void {
     this._logHandler(this, LogLevel.VERBOSE, ...args);
   }
-  info(...args): void {
+  info(...args: unknown[]): void {
     this._logHandler(this, LogLevel.INFO, ...args);
   }
-  warn(...args): void {
+  warn(...args: unknown[]): void {
     this._logHandler(this, LogLevel.WARN, ...args);
   }
-  error(...args): void {
+  error(...args: unknown[]): void {
     this._logHandler(this, LogLevel.ERROR, ...args);
   }
 }
diff --git a/packages/logger/test/logger.test.ts b/packages/logger/test/logger.test.ts
index 4fe2728aee3..65afa4a0477 100644
--- a/packages/logger/test/logger.test.ts
+++ b/packages/logger/test/logger.test.ts
@@ -46,7 +46,7 @@ describe('@firebase/logger', () => {
     spies.errorSpy.restore();
   });
 
-  function testLog(message, channel, shouldLog): void {
+  function testLog(message: string, channel: string, shouldLog: boolean): void {
     /**
      * Ensure that `debug` logs assert against the `console.log` function. The
      * rationale here is explained in `logger.ts`.
@@ -56,6 +56,7 @@ describe('@firebase/logger', () => {
     it(`Should ${
       shouldLog ? '' : 'not'
     } call \`console.${channel}\` if \`.${channel}\` is called`, () => {
+      // @ts-ignore It's not worth making a dedicated enum for a test.
       client[channel](message);
       expect(
         spies[`${channel}Spy`]!.called,
diff --git a/packages/rxfire/database/list/index.ts b/packages/rxfire/database/list/index.ts
index 28641eaf8eb..c7fee511f4c 100644
--- a/packages/rxfire/database/list/index.ts
+++ b/packages/rxfire/database/list/index.ts
@@ -69,7 +69,7 @@ export function listVal<T>(
   );
 }
 
-function positionFor(changes: QueryChange[], key) {
+function positionFor(changes: QueryChange[], key: string | null) {
   const len = changes.length;
   for (let i = 0; i < len; i++) {
     if (changes[i].snapshot.key === key) {
diff --git a/packages/rxfire/storage/index.ts b/packages/rxfire/storage/index.ts
index 4ad10af9963..6513c23c943 100644
--- a/packages/rxfire/storage/index.ts
+++ b/packages/rxfire/storage/index.ts
@@ -23,7 +23,7 @@ export function fromTask(task: storage.UploadTask) {
   return new Observable<storage.UploadTaskSnapshot>(subscriber => {
     const progress = (snap: storage.UploadTaskSnapshot) =>
       subscriber.next(snap);
-    const error = e => subscriber.error(e);
+    const error = (e: Error) => subscriber.error(e);
     const complete = () => subscriber.complete();
     task.on('state_changed', progress, error, complete);
     return () => task.cancel();
diff --git a/packages/rxfire/test/database.test.ts b/packages/rxfire/test/database.test.ts
index 2457cfd04da..a03b90f162e 100644
--- a/packages/rxfire/test/database.test.ts
+++ b/packages/rxfire/test/database.test.ts
@@ -30,11 +30,10 @@ const rando = () =>
     .toString(36)
     .substring(5);
 
-let batch = (items: any[]) => {
-  let batch = {};
-  Object.keys(items).forEach(function(key) {
-    const itemValue = items[key];
-    batch[itemValue.key] = itemValue;
+let batch = (items: { name: string; key: string }[]) => {
+  let batch: { [key: string]: unknown } = {};
+  items.forEach(item => {
+    batch[item.key] = item;
   });
   // make batch immutable to preserve integrity
   return Object.freeze(batch);
diff --git a/packages/rxfire/test/firestore.test.ts b/packages/rxfire/test/firestore.test.ts
index a9acda37c4e..f99af8ba628 100644
--- a/packages/rxfire/test/firestore.test.ts
+++ b/packages/rxfire/test/firestore.test.ts
@@ -52,7 +52,7 @@ const unwrapChange = map((changes: firestore.DocumentChange[]) => {
  * Create an environment for the tests to run in. The information is returned
  * from the function for use within the test.
  */
-const seedTest = firestore => {
+const seedTest = (firestore: firestore.Firestore) => {
   const colRef = createRandomCol(firestore);
   const davidDoc = colRef.doc('david');
   davidDoc.set({ name: 'David' });
diff --git a/packages/storage/index.ts b/packages/storage/index.ts
index b1d30ab0ddc..09e0d5aab43 100644
--- a/packages/storage/index.ts
+++ b/packages/storage/index.ts
@@ -17,7 +17,10 @@
 
 import firebase from '@firebase/app';
 import { FirebaseApp } from '@firebase/app-types';
-import { FirebaseServiceFactory } from '@firebase/app-types/private';
+import {
+  FirebaseServiceFactory,
+  _FirebaseNamespace
+} from '@firebase/app-types/private';
 import { StringFormat } from './src/implementation/string';
 import { TaskEvent } from './src/implementation/taskenums';
 import { TaskState } from './src/implementation/taskenums';
@@ -39,7 +42,7 @@ function factory(
   return new Service(app, new XhrIoPool(), opt_url) as any;
 }
 
-export function registerStorage(instance) {
+export function registerStorage(instance: _FirebaseNamespace) {
   let namespaceExports = {
     // no-inline
     TaskState: TaskState,
@@ -58,7 +61,7 @@ export function registerStorage(instance) {
   );
 }
 
-registerStorage(firebase);
+registerStorage(firebase as _FirebaseNamespace);
 
 /**
  * Define extension behavior for `registerStorage`
diff --git a/packages/storage/src/implementation/fs.ts b/packages/storage/src/implementation/fs.ts
index e216cb7b2d7..d49ea960948 100644
--- a/packages/storage/src/implementation/fs.ts
+++ b/packages/storage/src/implementation/fs.ts
@@ -21,10 +21,6 @@
  */
 import * as type from './type';
 
-declare var IBlobBuilder;
-declare var BlobBuilder;
-declare var WebKitBlobBuilder;
-
 function getBlobBuilder(): (typeof IBlobBuilder) | undefined {
   if (typeof BlobBuilder !== 'undefined') {
     return BlobBuilder;
diff --git a/packages/storage/src/implementation/requestinfo.ts b/packages/storage/src/implementation/requestinfo.ts
index b06b260df66..052954fcb97 100644
--- a/packages/storage/src/implementation/requestinfo.ts
+++ b/packages/storage/src/implementation/requestinfo.ts
@@ -17,7 +17,7 @@
 import { FirebaseStorageError } from './error';
 import { Headers, XhrIo } from './xhrio';
 
-export type UrlParams = { [name: string]: string };
+export type UrlParams = { [name: string]: string | number };
 
 export class RequestInfo<T> {
   urlParams: UrlParams = {};
diff --git a/packages/storage/src/implementation/requests.ts b/packages/storage/src/implementation/requests.ts
index ac63e997b25..d096709489c 100644
--- a/packages/storage/src/implementation/requests.ts
+++ b/packages/storage/src/implementation/requests.ts
@@ -163,7 +163,7 @@ export function list(
   pageToken?: string | null,
   maxResults?: number | null
 ): RequestInfo<ListResult> {
-  let urlParams = {};
+  let urlParams: UrlParams = {};
   if (location.isRoot) {
     urlParams['prefix'] = '';
   } else {
@@ -427,13 +427,13 @@ export function getResumableUploadStatus(
 
   function handler(xhr: XhrIo, text: string): ResumableUploadStatus {
     let status = checkResumeHeader_(xhr, ['active', 'final']);
-    let sizeString;
+    let sizeString: string | null = null;
     try {
       sizeString = xhr.getResponseHeader('X-Goog-Upload-Size-Received');
     } catch (e) {
       handlerCheck(false);
     }
-    let size = parseInt(sizeString, 10);
+    let size = parseInt(sizeString as string, 10);
     handlerCheck(!isNaN(size));
     return new ResumableUploadStatus(size, blob.size(), status === 'final');
   }
diff --git a/packages/storage/src/implementation/url.ts b/packages/storage/src/implementation/url.ts
index 52a0f1330ad..42160922e13 100644
--- a/packages/storage/src/implementation/url.ts
+++ b/packages/storage/src/implementation/url.ts
@@ -20,16 +20,17 @@
  */
 import * as object from './object';
 import { DEFAULT_HOST } from './constants';
+import { UrlParams } from './requestinfo';
 
 export function makeUrl(urlPart: string): string {
   return `https://${DEFAULT_HOST}/v0${urlPart}`;
 }
 
-export function makeQueryString(params: { [key: string]: string }): string {
+export function makeQueryString(params: UrlParams): string {
   let encode = encodeURIComponent;
   let queryPart = '?';
   object.forEach(params, function(key, val) {
-    let nextPart = encode(key) + '=' + encode(val);
+    let nextPart = encode(key) + '=' + encode(val.toString());
     queryPart = queryPart + nextPart + '&';
   });
 
diff --git a/packages/storage/test/reference.test.ts b/packages/storage/test/reference.test.ts
index e913b9cbaab..5d22cc177b8 100644
--- a/packages/storage/test/reference.test.ts
+++ b/packages/storage/test/reference.test.ts
@@ -32,7 +32,7 @@ function makeFakeService(app: FirebaseApp, sendHook: SendHook): Service {
 }
 
 function makeStorage(url: string): Reference {
-  function maker(wrapper, loc) {
+  function maker(wrapper: unknown, loc: unknown) {
     return ({} as any) as Reference;
   }
 
diff --git a/packages/storage/test/request.test.ts b/packages/storage/test/request.test.ts
index c609f7cccd2..ff6a99f613b 100644
--- a/packages/storage/test/request.test.ts
+++ b/packages/storage/test/request.test.ts
@@ -45,7 +45,7 @@ describe('Firebase Storage > Request', () => {
       body?: ArrayBufferView | Blob | string | null,
       headers?: Headers
     ) {
-      const responseHeaders = {};
+      const responseHeaders: Headers = {};
       responseHeaders[responseHeader] = responseValue;
       xhrio.simulateResponse(status, response, responseHeaders);
     }
@@ -75,7 +75,7 @@ describe('Firebase Storage > Request', () => {
           const args = spiedSend.getCall(0).args;
           assert.equal(args[1], url);
           assert.equal(args[2], method);
-          const expectedHeaders = {};
+          const expectedHeaders: Headers = {};
           expectedHeaders[requestHeader] = requestValue;
           expectedHeaders[versionHeaderName] = versionHeaderValue;
           assert.deepEqual(args[4], expectedHeaders);
@@ -224,7 +224,9 @@ describe('Firebase Storage > Request', () => {
       result => {
         assert.isTrue(spiedSend.calledOnce);
         const args = spiedSend.getCall(0).args;
-        const expectedHeaders = { Authorization: 'Firebase ' + authToken };
+        const expectedHeaders: Headers = {
+          Authorization: 'Firebase ' + authToken
+        };
         expectedHeaders[versionHeaderName] = versionHeaderValue;
         assert.deepEqual(args[4], expectedHeaders);
       },
diff --git a/packages/storage/test/task.test.ts b/packages/storage/test/task.test.ts
index e244e61ecee..85b9722021a 100644
--- a/packages/storage/test/task.test.ts
+++ b/packages/storage/test/task.test.ts
@@ -278,7 +278,7 @@ describe('Firebase Storage > Upload Task', () => {
 
     // This one will get executed immediately
     const h3: Unsubscribe = (() => {
-      let lastState;
+      let lastState: string;
       return task.on(
         TaskEvent.STATE_CHANGED,
         snapshot => {
@@ -324,7 +324,7 @@ describe('Firebase Storage > Upload Task', () => {
     );
     return fbsPromise.make<void>((resolve, reject) => {
       task.on(TaskEvent.STATE_CHANGED, {
-        error: err => {
+        error: (err: Error) => {
           assert.fail('Unexpected upload failure');
         },
         complete: () => {
@@ -344,7 +344,7 @@ describe('Firebase Storage > Upload Task', () => {
       blob
     );
 
-    let resolve, reject;
+    let resolve: Function, reject: Function;
     const promise = fbsPromise.make<void>(function(innerResolve, innerReject) {
       resolve = innerResolve;
       reject = innerReject;
@@ -375,8 +375,8 @@ describe('Firebase Storage > Upload Task', () => {
     const events: string[] = [];
     const progress: number[][] = [];
     let complete = 0;
-    function addCallbacks(task) {
-      let lastState;
+    function addCallbacks(task: UploadTask) {
+      let lastState: string;
       task.on(
         TaskEvent.STATE_CHANGED,
         snapshot => {
@@ -409,7 +409,7 @@ describe('Firebase Storage > Upload Task', () => {
     addCallbacks(task);
 
     (function() {
-      let lastState;
+      let lastState: string;
       task.on(TaskEvent.STATE_CHANGED, function(snapshot) {
         const state = snapshot.state;
         if (lastState !== TaskState.PAUSED && state === TaskState.PAUSED) {
@@ -467,7 +467,7 @@ describe('Firebase Storage > Upload Task', () => {
       const events2: string[] = [];
 
       (function() {
-        let lastState;
+        let lastState: string;
         task2.on(
           TaskEvent.STATE_CHANGED,
           snapshot => {
diff --git a/packages/storage/test/xhrio.ts b/packages/storage/test/xhrio.ts
index 33d2471f215..875c9d557cd 100644
--- a/packages/storage/test/xhrio.ts
+++ b/packages/storage/test/xhrio.ts
@@ -38,7 +38,7 @@ export type StringHeaders = { [name: string]: string };
 export class TestingXhrIo implements XhrIo {
   private state: State;
   private sendPromise: Promise<XhrIo>;
-  private resolve: (XhrIo) => void;
+  private resolve: (xhrIo: XhrIo) => void;
   private sendHook: SendHook | null;
   private status: number;
   private responseText: string;
@@ -121,10 +121,12 @@ export class TestingXhrIo implements XhrIo {
     }
   }
 
+  // @ts-ignore Remove when implemented.
   addUploadProgressListener(listener): void {
     // TODO(andysoto): impl
   }
 
+  // @ts-ignore Remove when implemented.
   removeUploadProgressListener(listener): void {
     // TODO(andysoto): impl
   }
diff --git a/packages/testing/src/api/index.ts b/packages/testing/src/api/index.ts
index ded08f5af8c..376dae6c3a0 100644
--- a/packages/testing/src/api/index.ts
+++ b/packages/testing/src/api/index.ts
@@ -115,7 +115,7 @@ function initializeApp(
   databaseName?: string,
   projectId?: string
 ): firebase.app.App {
-  let appOptions = {};
+  let appOptions: { [key: string]: string } = {};
   if (databaseName) {
     appOptions['databaseURL'] = `http://${DATABASE_ADDRESS}?ns=${databaseName}`;
   }
@@ -212,7 +212,8 @@ export function loadFirestoreRules(
         project: `projects/${options.projectId}`,
         rules: { files: [{ content: options.rules }] }
       },
-      (err, resp) => {
+      // @ts-ignore Defined in protobuf.
+      (err: Error, resp) => {
         if (err) {
           reject(err);
         } else {
@@ -247,7 +248,8 @@ export function clearFirestoreData(
       {
         database: `projects/${options.projectId}/databases/(default)`
       },
-      (err, resp) => {
+      // @ts-ignore Defined in protobuf.
+      (err: Error, resp) => {
         if (err) {
           reject(err);
         } else {
diff --git a/packages/util/src/assert.ts b/packages/util/src/assert.ts
index a55f2c5410e..dc77d9fe232 100644
--- a/packages/util/src/assert.ts
+++ b/packages/util/src/assert.ts
@@ -19,10 +19,8 @@ import { CONSTANTS } from './constants';
 
 /**
  * Throws an error if the provided assertion is falsy
- * @param {*} assertion The assertion to be tested for falsiness
- * @param {!string} message The message to display if the check fails
  */
-export const assert = function(assertion, message): void {
+export const assert = function(assertion: unknown, message: string): void {
   if (!assertion) {
     throw assertionError(message);
   }
@@ -30,10 +28,8 @@ export const assert = function(assertion, message): void {
 
 /**
  * Returns an Error object suitable for throwing.
- * @param {string} message
- * @return {!Error}
  */
-export const assertionError = function(message): Error {
+export const assertionError = function(message: string): Error {
   return new Error(
     'Firebase Database (' +
       CONSTANTS.SDK_VERSION +
diff --git a/packages/util/src/crypt.ts b/packages/util/src/crypt.ts
index 9eb1ede54ec..4b9f38fe374 100644
--- a/packages/util/src/crypt.ts
+++ b/packages/util/src/crypt.ts
@@ -15,7 +15,7 @@
  * limitations under the License.
  */
 
-const stringToByteArray = function(str): number[] {
+const stringToByteArray = function(str: string): number[] {
   // TODO(user): Use native implementations if/when available
   const out: number[] = [];
   let p = 0;
@@ -52,7 +52,7 @@ const stringToByteArray = function(str): number[] {
  * @param bytes Array of numbers representing characters.
  * @return Stringification of the array.
  */
-const byteArrayToString = function(bytes): string {
+const byteArrayToString = function(bytes: number[]): string {
   // TODO(user): Use native implementations if/when available
   const out: string[] = [];
   let pos = 0,
diff --git a/packages/util/src/deepCopy.ts b/packages/util/src/deepCopy.ts
index 8a265f45c59..0f64fede639 100644
--- a/packages/util/src/deepCopy.ts
+++ b/packages/util/src/deepCopy.ts
@@ -66,9 +66,9 @@ export function deepExtend(target: unknown, source: unknown): unknown {
     if (!source.hasOwnProperty(prop)) {
       continue;
     }
-    (target as object)[prop] = deepExtend(
-      (target as object)[prop],
-      source[prop]
+    (target as { [key: string]: unknown })[prop] = deepExtend(
+      (target as { [key: string]: unknown })[prop],
+      (source as { [key: string]: unknown })[prop]
     );
   }
 
diff --git a/packages/util/src/deferred.ts b/packages/util/src/deferred.ts
index 4a8a24aaf95..8a40afa7c29 100644
--- a/packages/util/src/deferred.ts
+++ b/packages/util/src/deferred.ts
@@ -17,8 +17,8 @@
 
 export class Deferred<R> {
   promise: Promise<R>;
-  reject;
-  resolve;
+  reject: (value?: unknown) => void;
+  resolve: (value?: unknown) => void;
   constructor() {
     this.promise = new Promise((resolve, reject) => {
       this.resolve = resolve;
@@ -30,10 +30,10 @@ export class Deferred<R> {
    * Our API internals are not promiseified and cannot because our callback APIs have subtle expectations around
    * invoking promises inline, which Promises are forbidden to do. This method accepts an optional node-style callback
    * and returns a node-style callback which will resolve or reject the Deferred's promise.
-   * @param {((?function(?(Error)): (?|undefined))| (?function(?(Error),?=): (?|undefined)))=} callback
-   * @return {!function(?(Error), ?=)}
    */
-  wrapCallback(callback?): (error: unknown, value?: unknown) => void {
+  wrapCallback(
+    callback?: (error?: unknown, value?: unknown) => void
+  ): (error: unknown, value?: unknown) => void {
     return (error, value?) => {
       if (error) {
         this.reject(error);
diff --git a/packages/util/src/environment.ts b/packages/util/src/environment.ts
index 0e33b246db7..512a3368f05 100644
--- a/packages/util/src/environment.ts
+++ b/packages/util/src/environment.ts
@@ -42,6 +42,8 @@ export function getUA(): string {
 export function isMobileCordova(): boolean {
   return (
     typeof window !== 'undefined' &&
+    // @ts-ignore Setting up an broadly applicable index signature for Window
+    // just to deal with this case would probably be a bad idea.
     !!(window['cordova'] || window['phonegap'] || window['PhoneGap']) &&
     /ios|iphone|ipod|ipad|android|blackberry|iemobile/i.test(getUA())
   );
diff --git a/packages/util/src/jwt.ts b/packages/util/src/jwt.ts
index 7f04ef5394a..f5fd1cf47c7 100644
--- a/packages/util/src/jwt.ts
+++ b/packages/util/src/jwt.ts
@@ -18,26 +18,34 @@
 import { base64Decode } from './crypt';
 import { jsonEval } from './json';
 
+interface Claims {
+  [key: string]: {};
+}
+
+interface DecodedToken {
+  header: object;
+  claims: Claims;
+  data: object;
+  signature: string;
+}
+
 /**
  * Decodes a Firebase auth. token into constituent parts.
  *
  * Notes:
  * - May return with invalid / incomplete claims if there's no native base64 decoding support.
  * - Doesn't check if the token is actually valid.
- *
- * @param {?string} token
- * @return {{header: *, claims: *, data: *, signature: string}}
  */
-export const decode = function(token): DecodedToken {
+export const decode = function(token: string): DecodedToken {
   let header = {},
-    claims = {},
+    claims: Claims = {},
     data = {},
     signature = '';
 
   try {
     const parts = token.split('.');
     header = jsonEval(base64Decode(parts[0]) || '') as object;
-    claims = jsonEval(base64Decode(parts[1]) || '') as object;
+    claims = jsonEval(base64Decode(parts[1]) || '') as Claims;
     signature = parts[2];
     data = claims['d'] || {};
     delete claims['d'];
@@ -53,7 +61,7 @@ export const decode = function(token): DecodedToken {
 
 interface DecodedToken {
   header: object;
-  claims: object;
+  claims: Claims;
   data: object;
   signature: string;
 }
@@ -65,24 +73,22 @@ interface DecodedToken {
  * Notes:
  * - May return a false negative if there's no native base64 decoding support.
  * - Doesn't check if the token is actually valid.
- *
- * @param {?string} token
- * @return {boolean}
  */
-export const isValidTimestamp = function(token): boolean {
-  const claims = decode(token).claims,
-    now = Math.floor(new Date().getTime() / 1000);
-  let validSince, validUntil;
+export const isValidTimestamp = function(token: string): boolean {
+  const claims: Claims = decode(token).claims;
+  const now: number = Math.floor(new Date().getTime() / 1000);
+  let validSince: number = 0,
+    validUntil: number = 0;
 
   if (typeof claims === 'object') {
     if (claims.hasOwnProperty('nbf')) {
-      validSince = claims['nbf'];
+      validSince = claims['nbf'] as number;
     } else if (claims.hasOwnProperty('iat')) {
-      validSince = claims['iat'];
+      validSince = claims['iat'] as number;
     }
 
     if (claims.hasOwnProperty('exp')) {
-      validUntil = claims['exp'];
+      validUntil = claims['exp'] as number;
     } else {
       // token will expire after 24h by default
       validUntil = validSince + 86400;
@@ -90,7 +96,11 @@ export const isValidTimestamp = function(token): boolean {
   }
 
   return (
-    now && validSince && validUntil && now >= validSince && now <= validUntil
+    !!now &&
+    !!validSince &&
+    !!validUntil &&
+    now >= validSince &&
+    now <= validUntil
   );
 };
 
@@ -100,14 +110,11 @@ export const isValidTimestamp = function(token): boolean {
  * Notes:
  * - May return null if there's no native base64 decoding support.
  * - Doesn't check if the token is actually valid.
- *
- * @param {?string} token
- * @return {?number}
  */
-export const issuedAtTime = function(token): number | null {
-  const claims = decode(token).claims;
+export const issuedAtTime = function(token: string): number | null {
+  const claims: Claims = decode(token).claims;
   if (typeof claims === 'object' && claims.hasOwnProperty('iat')) {
-    return claims['iat'];
+    return claims['iat'] as number;
   }
   return null;
 };
@@ -118,11 +125,8 @@ export const issuedAtTime = function(token): number | null {
  * Notes:
  * - May return a false negative if there's no native base64 decoding support.
  * - Doesn't check if the token is actually valid.
- *
- * @param {?string} token
- * @return {boolean}
  */
-export const isValidFormat = function(token): boolean {
+export const isValidFormat = function(token: string): boolean {
   const decoded = decode(token),
     claims = decoded.claims;
 
@@ -135,11 +139,8 @@ export const isValidFormat = function(token): boolean {
  * Notes:
  * - May return a false negative if there's no native base64 decoding support.
  * - Doesn't check if the token is actually valid.
- *
- * @param {?string} token
- * @return {boolean}
  */
-export const isAdmin = function(token): boolean {
-  const claims = decode(token).claims;
+export const isAdmin = function(token: string): boolean {
+  const claims: Claims = decode(token).claims;
   return typeof claims === 'object' && claims['admin'] === true;
 };
diff --git a/packages/util/src/obj.ts b/packages/util/src/obj.ts
index 61b6526c496..c5b20dd68a2 100644
--- a/packages/util/src/obj.ts
+++ b/packages/util/src/obj.ts
@@ -18,12 +18,19 @@
 /* eslint-disable */
 // will enable after https://github.com/firebase/firebase-js-sdk/pull/1811 is merged
 
+interface UtilObject<V> {
+  [key: string]: V;
+}
+
 // See http://www.devthought.com/2012/01/18/an-object-is-not-a-hash/
-export const contains = function(obj, key) {
+export const contains = function<V>(obj: UtilObject<V>, key: string): boolean {
   return Object.prototype.hasOwnProperty.call(obj, key);
 };
 
-export const safeGet = function(obj, key) {
+export const safeGet = function<V>(
+  obj: UtilObject<V>,
+  key: string
+): V | undefined {
   if (Object.prototype.hasOwnProperty.call(obj, key)) return obj[key];
   // else return undefined.
 };
@@ -35,8 +42,11 @@ export const safeGet = function(obj, key) {
  * @param {!function(K, V)} fn Function to call for each key and value.
  * @template K,V
  */
-export const forEach = function(obj, fn) {
-  for (var key in obj) {
+export const forEach = function<V>(
+  obj: UtilObject<V>,
+  fn: (key: string, value: V) => void
+): void {
+  for (const key in obj) {
     if (Object.prototype.hasOwnProperty.call(obj, key)) {
       fn(key, obj[key]);
     }
@@ -49,7 +59,10 @@ export const forEach = function(obj, fn) {
  * @param {!Object} objFrom
  * @return {!Object} objTo
  */
-export const extend = function(objTo, objFrom) {
+export const extend = function<V>(
+  objTo: UtilObject<V>,
+  objFrom: UtilObject<V>
+): UtilObject<V> {
   forEach(objFrom, function(key, value) {
     objTo[key] = value;
   });
@@ -61,29 +74,26 @@ export const extend = function(objTo, objFrom) {
  * @param {!Object} obj
  * @return {!Object} cloned obj.
  */
-export const clone = function(obj) {
+export const clone = function<V>(obj: UtilObject<V>) {
   return extend({}, obj);
 };
 
 /**
  * Returns true if obj has typeof "object" and is not null.  Unlike goog.isObject(), does not return true
  * for functions.
- *
- * @param obj {*} A potential object.
- * @returns {boolean} True if it's an object.
  */
-export const isNonNullObject = function(obj) {
+export const isNonNullObject = function<V>(obj: UtilObject<V>): boolean {
   return typeof obj === 'object' && obj !== null;
 };
 
-export const isEmpty = function(obj) {
+export const isEmpty = function<V>(obj: UtilObject<V>) {
   for (var key in obj) {
     return false;
   }
   return true;
 };
 
-export const getCount = function(obj) {
+export const getCount = function<V>(obj: UtilObject<V>): number {
   var rv = 0;
   for (var key in obj) {
     rv++;
@@ -91,36 +101,48 @@ export const getCount = function(obj) {
   return rv;
 };
 
-export const map = function(obj, f, opt_obj?) {
-  var res = {};
+export const map = function<V>(
+  obj: UtilObject<V>,
+  fn: (value: V, key: string | number, obj: UtilObject<V>) => unknown,
+  context?: unknown
+) {
+  var res: UtilObject<V> = {};
   for (var key in obj) {
-    res[key] = f.call(opt_obj, obj[key], key, obj);
+    res[key] = fn.call(context, obj[key], key, obj);
   }
   return res;
 };
 
-export const findKey = function(obj, fn, opt_this?) {
+export const findKey = function<V>(
+  obj: UtilObject<V>,
+  fn: (value: V, key: string | number, obj: UtilObject<V>) => unknown,
+  context?: unknown
+) {
   for (var key in obj) {
-    if (fn.call(opt_this, obj[key], key, obj)) {
+    if (fn.call(context, obj[key], key, obj)) {
       return key;
     }
   }
   return undefined;
 };
 
-export const findValue = function(obj, fn, opt_this?) {
-  var key = findKey(obj, fn, opt_this);
+export const findValue = function<V>(
+  obj: UtilObject<V>,
+  fn: (value: V, key: string | number, obj: UtilObject<V>) => unknown,
+  context?: unknown
+) {
+  var key = findKey(obj, fn, context);
   return key && obj[key];
 };
 
-export const getAnyKey = function(obj) {
+export const getAnyKey = function<V>(obj: UtilObject<V>) {
   for (var key in obj) {
     return key;
   }
 };
 
-export const getValues = function(obj) {
-  var res: any[] = [];
+export const getValues = function<V>(obj: UtilObject<V>) {
+  var res: V[] = [];
   var i = 0;
   for (var key in obj) {
     res[i++] = obj[key];
@@ -137,7 +159,7 @@ export const getValues = function(obj) {
  * @template K,V
  */
 export const every = function<V>(
-  obj: Object,
+  obj: UtilObject<V>,
   fn: (k: string, v?: V) => boolean
 ): boolean {
   for (let key in obj) {
diff --git a/packages/util/src/query.ts b/packages/util/src/query.ts
index bb547cacb1a..1c766bb6935 100644
--- a/packages/util/src/query.ts
+++ b/packages/util/src/query.ts
@@ -21,13 +21,12 @@ import { forEach } from './obj';
  * Returns a querystring-formatted string (e.g. &arg=val&arg2=val2) from a params
  * object (e.g. {arg: 'val', arg2: 'val2'})
  * Note: You must prepend it with ? when adding it to a URL.
- *
- * @param {!Object} querystringParams
- * @return {string}
  */
-export const querystring = function(querystringParams): string {
+export const querystring = function<V>(querystringParams: {
+  [key: string]: string;
+}): string {
   const params: string[] = [];
-  forEach(querystringParams, (key, value) => {
+  forEach(querystringParams, (key: string, value) => {
     if (Array.isArray(value)) {
       value.forEach(arrayVal => {
         params.push(
@@ -47,8 +46,8 @@ export const querystring = function(querystringParams): string {
  * @param {string} querystring
  * @return {!Object}
  */
-export const querystringDecode = function(querystring): object {
-  const obj = {};
+export const querystringDecode = function(querystring: string): object {
+  const obj: { [key: string]: unknown } = {};
   const tokens = querystring.replace(/^\?/, '').split('&');
 
   tokens.forEach(token => {
diff --git a/packages/util/src/sha1.ts b/packages/util/src/sha1.ts
index cf5fc097439..0054ff86ca6 100644
--- a/packages/util/src/sha1.ts
+++ b/packages/util/src/sha1.ts
@@ -102,13 +102,13 @@ export class Sha1 {
 
   /**
    * Internal compress helper function.
-   * @param {!number[]|!Uint8Array|string} buf Block to compress.
-   * @param {number=} optOffset Offset of the block in the buffer.
+   * @param buf Block to compress.
+   * @param offset Offset of the block in the buffer.
    * @private
    */
-  compress_(buf, optOffset?): void {
-    if (!optOffset) {
-      optOffset = 0;
+  compress_(buf: number[] | Uint8Array | string, offset?: number): void {
+    if (!offset) {
+      offset = 0;
     }
 
     const W = this.W_;
@@ -125,20 +125,20 @@ export class Sha1 {
         // (https://bugs.webkit.org/show_bug.cgi?id=109036) has been fixed and
         // most clients have been updated.
         W[i] =
-          (buf.charCodeAt(optOffset) << 24) |
-          (buf.charCodeAt(optOffset + 1) << 16) |
-          (buf.charCodeAt(optOffset + 2) << 8) |
-          buf.charCodeAt(optOffset + 3);
-        optOffset += 4;
+          (buf.charCodeAt(offset) << 24) |
+          (buf.charCodeAt(offset + 1) << 16) |
+          (buf.charCodeAt(offset + 2) << 8) |
+          buf.charCodeAt(offset + 3);
+        offset += 4;
       }
     } else {
       for (let i = 0; i < 16; i++) {
         W[i] =
-          (buf[optOffset] << 24) |
-          (buf[optOffset + 1] << 16) |
-          (buf[optOffset + 2] << 8) |
-          buf[optOffset + 3];
-        optOffset += 4;
+          (buf[offset] << 24) |
+          (buf[offset + 1] << 16) |
+          (buf[offset + 2] << 8) |
+          buf[offset + 3];
+        offset += 4;
       }
     }
 
@@ -190,24 +190,24 @@ export class Sha1 {
     this.chain_[4] = (this.chain_[4] + e) & 0xffffffff;
   }
 
-  update(bytes, optLength?): void {
+  update(bytes?: number[] | Uint8Array | string, length?: number): void {
     // TODO(johnlenz): tighten the function signature and remove this check
     if (bytes == null) {
       return;
     }
 
-    if (optLength === undefined) {
-      optLength = bytes.length;
+    if (length === undefined) {
+      length = bytes.length;
     }
 
-    const lengthMinusBlock = optLength - this.blockSize;
+    const lengthMinusBlock = length - this.blockSize;
     let n = 0;
     // Using local instead of member variables gives ~5% speedup on Firefox 16.
     const buf = this.buf_;
     let inbuf = this.inbuf_;
 
     // The outer while loop should execute at most twice.
-    while (n < optLength) {
+    while (n < length) {
       // When we have no data in the block to top up, we can directly process the
       // input buffer (assuming it contains sufficient data). This gives ~25%
       // speedup on Chrome 23 and ~15% speedup on Firefox 16, but requires that
@@ -220,7 +220,7 @@ export class Sha1 {
       }
 
       if (typeof bytes === 'string') {
-        while (n < optLength) {
+        while (n < length) {
           buf[inbuf] = bytes.charCodeAt(n);
           ++inbuf;
           ++n;
@@ -232,7 +232,7 @@ export class Sha1 {
           }
         }
       } else {
-        while (n < optLength) {
+        while (n < length) {
           buf[inbuf] = bytes[n];
           ++inbuf;
           ++n;
@@ -247,7 +247,7 @@ export class Sha1 {
     }
 
     this.inbuf_ = inbuf;
-    this.total_ += optLength;
+    this.total_ += length;
   }
 
   /** @override */
diff --git a/packages/util/src/subscribe.ts b/packages/util/src/subscribe.ts
index d705f62293e..70e976ec3f1 100644
--- a/packages/util/src/subscribe.ts
+++ b/packages/util/src/subscribe.ts
@@ -272,7 +272,10 @@ export function async(fn: Function, onError?: ErrorFn): Function {
 /**
  * Return true if the object passed in implements any of the named methods.
  */
-function implementsAnyMethods(obj: unknown, methods: string[]): boolean {
+function implementsAnyMethods(
+  obj: { [key: string]: unknown },
+  methods: string[]
+): boolean {
   if (typeof obj !== 'object' || obj === null) {
     return false;
   }
diff --git a/packages/util/src/utf8.ts b/packages/util/src/utf8.ts
index 85ab3784939..4431727cf28 100644
--- a/packages/util/src/utf8.ts
+++ b/packages/util/src/utf8.ts
@@ -32,7 +32,7 @@ import { assert } from './assert';
  * @param {string} str
  * @return {Array}
  */
-export const stringToByteArray = function(str): number[] {
+export const stringToByteArray = function(str: string): number[] {
   const out: number[] = [];
   let p = 0;
   for (let i = 0; i < str.length; i++) {
@@ -71,7 +71,7 @@ export const stringToByteArray = function(str): number[] {
  * @param {string} str
  * @return {number}
  */
-export const stringLength = function(str): number {
+export const stringLength = function(str: string): number {
   let p = 0;
   for (let i = 0; i < str.length; i++) {
     const c = str.charCodeAt(i);
diff --git a/packages/util/src/validation.ts b/packages/util/src/validation.ts
index a368f09359e..48e985699a6 100644
--- a/packages/util/src/validation.ts
+++ b/packages/util/src/validation.ts
@@ -19,16 +19,16 @@
  * Check to make sure the appropriate number of arguments are provided for a public function.
  * Throws an error if it fails.
  *
- * @param {!string} fnName The function name
- * @param {!number} minCount The minimum number of arguments to allow for the function call
- * @param {!number} maxCount The maximum number of argument to allow for the function call
- * @param {!number} argCount The actual number of arguments provided.
+ * @param fnName The function name
+ * @param minCount The minimum number of arguments to allow for the function call
+ * @param maxCount The maximum number of argument to allow for the function call
+ * @param argCount The actual number of arguments provided.
  */
 export const validateArgCount = function(
-  fnName,
-  minCount,
-  maxCount,
-  argCount
+  fnName: string,
+  minCount: number,
+  maxCount: number,
+  argCount: number
 ): void {
   let argError;
   if (argCount < minCount) {
@@ -52,12 +52,16 @@ export const validateArgCount = function(
 /**
  * Generates a string to prefix an error message about failed argument validation
  *
- * @param {!string} fnName The function name
- * @param {!number} argumentNumber The index of the argument
- * @param {boolean} optional Whether or not the argument is optional
- * @return {!string} The prefix to add to the error thrown for validation.
+ * @param fnName The function name
+ * @param argumentNumber The index of the argument
+ * @param optional Whether or not the argument is optional
+ * @return The prefix to add to the error thrown for validation.
  */
-export function errorPrefix(fnName, argumentNumber, optional): string {
+export function errorPrefix(
+  fnName: string,
+  argumentNumber: number,
+  optional: boolean
+): string {
   let argName = '';
   switch (argumentNumber) {
     case 1:
@@ -85,16 +89,16 @@ export function errorPrefix(fnName, argumentNumber, optional): string {
 }
 
 /**
- * @param {!string} fnName
- * @param {!number} argumentNumber
- * @param {!string} namespace
- * @param {boolean} optional
+ * @param fnName
+ * @param argumentNumber
+ * @param namespace
+ * @param optional
  */
 export function validateNamespace(
-  fnName,
-  argumentNumber,
-  namespace,
-  optional
+  fnName: string,
+  argumentNumber: number,
+  namespace: string,
+  optional: boolean
 ): void {
   if (optional && !namespace) {
     return;
@@ -109,10 +113,10 @@ export function validateNamespace(
 }
 
 export function validateCallback(
-  fnName,
-  argumentNumber,
-  callback,
-  optional
+  fnName: string,
+  argumentNumber: number,
+  callback: Function,
+  optional: boolean
 ): void {
   if (optional && !callback) {
     return;
@@ -126,10 +130,10 @@ export function validateCallback(
 }
 
 export function validateContextObject(
-  fnName,
-  argumentNumber,
-  context,
-  optional
+  fnName: string,
+  argumentNumber: number,
+  context: unknown,
+  optional: boolean
 ): void {
   if (optional && !context) {
     return;
diff --git a/packages/webchannel-wrapper/package.json b/packages/webchannel-wrapper/package.json
index c1d5e1b485b..93595bd5410 100644
--- a/packages/webchannel-wrapper/package.json
+++ b/packages/webchannel-wrapper/package.json
@@ -26,6 +26,7 @@
     "type": "git",
     "url": "https://github.com/firebase/firebase-js-sdk.git"
   },
+  "typings": "src/index.d.ts",
   "bugs": {
     "url": "https://github.com/firebase/firebase-js-sdk/issues"
   }
diff --git a/packages/webchannel-wrapper/src/index.d.ts b/packages/webchannel-wrapper/src/index.d.ts
new file mode 100644
index 00000000000..4aedb1a7c8b
--- /dev/null
+++ b/packages/webchannel-wrapper/src/index.d.ts
@@ -0,0 +1,56 @@
+/**
+ * @license
+ * Copyright 2019 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// TODO(mikelehen): Flesh out proper types (or figure out how to generate via
+// clutz or something).
+export class XhrIo {}
+export const ErrorCode: any;
+export const EventType: any;
+export namespace WebChannel {
+  export type EventType = any;
+  export const EventType: any;
+}
+
+type StringMap = { [key: string]: string };
+
+export interface WebChannelOptions {
+  messageHeaders?: StringMap;
+  initMessageHeaders?: StringMap;
+  messageContentType?: string;
+  messageUrlParams?: StringMap;
+  clientProtocolHeaderRequired?: boolean;
+  concurrentRequestLimit?: number;
+  supportsCrossDomainXhr?: boolean;
+  testUrl?: string;
+  sendRawJson?: boolean;
+  httpSessionIdParam?: string;
+  httpHeadersOverwriteParam?: string;
+  backgroundChannelTest?: boolean;
+  forceLongPolling?: boolean;
+  fastHandshake?: boolean;
+  disableRedac?: boolean;
+  clientProfile?: string;
+  internalChannelParams?: { [key: string]: boolean | number };
+  xmlHttpFactory?: unknown;
+  requestRefreshThresholds?: { [key: string]: number };
+}
+
+export interface WebChannelTransport {
+  createWebChannel(url: string, options: WebChannelOptions): any;
+}
+
+export function createWebChannelTransport(): WebChannelTransport;
diff --git a/scripts/emulator-testing/emulators/emulator.ts b/scripts/emulator-testing/emulators/emulator.ts
index 0437d7e2c3c..fd5904794c7 100644
--- a/scripts/emulator-testing/emulators/emulator.ts
+++ b/scripts/emulator-testing/emulators/emulator.ts
@@ -15,11 +15,13 @@
  * limitations under the License.
  */
 
+// @ts-ignore
 import { spawn } from 'child-process-promise';
 import { ChildProcess } from 'child_process';
 import * as fs from 'fs';
 import * as path from 'path';
 import * as request from 'request';
+// @ts-ignore
 import * as tmp from 'tmp';
 
 export interface ChildProcessPromise extends Promise<void> {
@@ -40,7 +42,7 @@ export abstract class Emulator {
 
   download(): Promise<void> {
     return new Promise<void>((resolve, reject) => {
-      tmp.dir((err, dir) => {
+      tmp.dir((err: Error, dir: string) => {
         if (err) reject(err);
 
         console.log(`Created temporary directory at [${dir}].`);
@@ -89,7 +91,7 @@ export abstract class Emulator {
       const timeout = process.env.TRAVIS ? 100 : 30; // seconds
       const start: number = Date.now();
 
-      const wait = (resolve, reject) => {
+      const wait = (resolve: () => void, reject: (arg0: unknown) => void) => {
         const elapsed = (Date.now() - start) / 1000;
         if (elapsed > timeout) {
           reject(`Emulator not ready after ${timeout}s. Exiting ...`);
diff --git a/scripts/emulator-testing/emulators/firestore-emulator.ts b/scripts/emulator-testing/emulators/firestore-emulator.ts
index 4e82cb7ec39..aa4d68e4576 100644
--- a/scripts/emulator-testing/emulators/firestore-emulator.ts
+++ b/scripts/emulator-testing/emulators/firestore-emulator.ts
@@ -20,7 +20,7 @@ import { Emulator } from './emulator';
 export class FirestoreEmulator extends Emulator {
   projectId: string;
 
-  constructor(port, projectId = 'test-emulator') {
+  constructor(port: number, projectId = 'test-emulator') {
     super(port);
     this.projectId = projectId;
     this.binaryName = 'firestore-emulator.jar';
diff --git a/scripts/emulator-testing/firestore-test-runner.ts b/scripts/emulator-testing/firestore-test-runner.ts
index c3a8669e657..4cfdf55f36f 100644
--- a/scripts/emulator-testing/firestore-test-runner.ts
+++ b/scripts/emulator-testing/firestore-test-runner.ts
@@ -15,8 +15,10 @@
  * limitations under the License.
  */
 
+// @ts-ignore
 import { spawn } from 'child-process-promise';
 import * as path from 'path';
+// @ts-ignore
 import * as freePortFinder from 'find-free-port';
 
 import { ChildProcessPromise } from './emulators/emulator';
@@ -48,9 +50,9 @@ async function run(): Promise<void> {
   }
 }
 
-function findFreePort() {
+function findFreePort(): Promise<number> {
   return new Promise((resolve, reject) => {
-    freePortFinder(10000, (err, port) => {
+    freePortFinder(10000, (err: Error, port: number) => {
       return err ? reject(err) : resolve(port);
     });
   });