diff --git a/packages/firestore/src/local/indexeddb_persistence.ts b/packages/firestore/src/local/indexeddb_persistence.ts
index c4bcd5c8634..b09548e5e2b 100644
--- a/packages/firestore/src/local/indexeddb_persistence.ts
+++ b/packages/firestore/src/local/indexeddb_persistence.ts
@@ -25,8 +25,13 @@ import { AutoId } from '../util/misc';
 import { IndexedDbMutationQueue } from './indexeddb_mutation_queue';
 import { IndexedDbQueryCache } from './indexeddb_query_cache';
 import { IndexedDbRemoteDocumentCache } from './indexeddb_remote_document_cache';
-import { ALL_STORES, DbOwner, DbOwnerKey } from './indexeddb_schema';
-import { createOrUpgradeDb, SCHEMA_VERSION } from './indexeddb_schema';
+import {
+  ALL_STORES,
+  createOrUpgradeDb,
+  DbOwner,
+  DbOwnerKey,
+  SCHEMA_VERSION
+} from './indexeddb_schema';
 import { LocalSerializer } from './local_serializer';
 import { MutationQueue } from './mutation_queue';
 import { Persistence } from './persistence';
diff --git a/packages/firestore/src/local/indexeddb_schema.ts b/packages/firestore/src/local/indexeddb_schema.ts
index 88bfb484371..d3689ff94f1 100644
--- a/packages/firestore/src/local/indexeddb_schema.ts
+++ b/packages/firestore/src/local/indexeddb_schema.ts
@@ -22,53 +22,48 @@ import { assert } from '../util/assert';
 
 import { encode, EncodedResourcePath } from './encoded_resource_path';
 
-export const SCHEMA_VERSION = 1;
-
-/** Performs database creation and (in the future) upgrades between versions. */
-export function createOrUpgradeDb(db: IDBDatabase, oldVersion: number): void {
-  assert(oldVersion === 0, 'Unexpected upgrade from version ' + oldVersion);
-
-  db.createObjectStore(DbMutationQueue.store, {
-    keyPath: DbMutationQueue.keyPath
-  });
-
-  // TODO(mikelehen): Get rid of "as any" if/when TypeScript fixes their
-  // types. https://github.com/Microsoft/TypeScript/issues/14322
-  db.createObjectStore(
-    DbMutationBatch.store,
-    // tslint:disable-next-line:no-any
-    { keyPath: DbMutationBatch.keyPath as any }
-  );
+/**
+ * Schema Version for the Web client (containing the Mutation Queue, the Query
+ * and the Remote Document Cache) and Multi-Tab Support.
+ */
+export const SCHEMA_VERSION = 2;
 
-  const targetDocumentsStore = db.createObjectStore(
-    DbTargetDocument.store,
-    // tslint:disable-next-line:no-any
-    { keyPath: DbTargetDocument.keyPath as any }
-  );
-  targetDocumentsStore.createIndex(
-    DbTargetDocument.documentTargetsIndex,
-    DbTargetDocument.documentTargetsKeyPath,
-    { unique: true }
+/**
+ * Performs database creation and schema upgrades.
+ *
+ * Note that in production, this method is only ever used to upgrade the schema
+ * to SCHEMA_VERSION. Different versions are only used for testing and
+ * local feature development.
+ */
+export function createOrUpgradeDb(
+  db: IDBDatabase,
+  fromVersion: number,
+  toVersion: number
+): void {
+  // This function currently supports migrating to schema version 1 (Mutation
+  // Queue, Query and Remote Document Cache) and schema version 2 (Multi-Tab).
+  assert(
+    fromVersion < toVersion && fromVersion >= 0 && toVersion <= 2,
+    'Unexpected schema upgrade from v${fromVersion} to v{toVersion}.'
   );
 
-  const targetStore = db.createObjectStore(DbTarget.store, {
-    keyPath: DbTarget.keyPath
-  });
-  // NOTE: This is unique only because the TargetId is the suffix.
-  targetStore.createIndex(
-    DbTarget.queryTargetsIndexName,
-    DbTarget.queryTargetsKeyPath,
-    { unique: true }
-  );
+  if (fromVersion < 1 && toVersion >= 1) {
+    createOwnerStore(db);
+    createMutationQueue(db);
+    createQueryCache(db);
+    createRemoteDocumentCache(db);
+  }
 
-  // NOTE: keys for these stores are specified explicitly rather than using a
-  // keyPath.
-  db.createObjectStore(DbDocumentMutation.store);
-  db.createObjectStore(DbRemoteDocument.store);
-  db.createObjectStore(DbOwner.store);
-  db.createObjectStore(DbTargetGlobal.store);
+  if (fromVersion < 2 && toVersion >= 2) {
+    createClientMetadataStore(db);
+    createTargetChangeStore(db);
+  }
 }
 
+// TODO(mikelehen): Get rid of "as any" if/when TypeScript fixes their types.
+// https://github.com/Microsoft/TypeScript/issues/14322
+type KeyPath = any; // tslint:disable-line:no-any
+
 /**
  * Wrapper class to store timestamps (seconds and nanos) in IndexedDb objects.
  */
@@ -94,6 +89,10 @@ export class DbOwner {
   constructor(public ownerId: string, public leaseTimestampMs: number) {}
 }
 
+function createOwnerStore(db: IDBDatabase): void {
+  db.createObjectStore(DbOwner.store);
+}
+
 /** Object keys in the 'mutationQueues' store are userId strings. */
 export type DbMutationQueueKey = string;
 
@@ -183,6 +182,18 @@ export class DbMutationBatch {
  */
 export type DbDocumentMutationKey = [string, EncodedResourcePath, BatchId];
 
+function createMutationQueue(db: IDBDatabase): void {
+  db.createObjectStore(DbMutationQueue.store, {
+    keyPath: DbMutationQueue.keyPath
+  });
+
+  db.createObjectStore(DbMutationBatch.store, {
+    keyPath: DbMutationBatch.keyPath as KeyPath
+  });
+
+  db.createObjectStore(DbDocumentMutation.store);
+}
+
 /**
  * An object to be stored in the 'documentMutations' store in IndexedDb.
  *
@@ -241,6 +252,10 @@ export class DbDocumentMutation {
  */
 export type DbRemoteDocumentKey = string[];
 
+function createRemoteDocumentCache(db: IDBDatabase): void {
+  db.createObjectStore(DbRemoteDocument.store);
+}
+
 /**
  * Represents the known absence of a document at a particular version.
  * Stored in IndexedDb as part of a DbRemoteDocument object.
@@ -455,11 +470,101 @@ export class DbTargetGlobal {
   ) {}
 }
 
+function createQueryCache(db: IDBDatabase): void {
+  const targetDocumentsStore = db.createObjectStore(DbTargetDocument.store, {
+    keyPath: DbTargetDocument.keyPath as KeyPath
+  });
+  targetDocumentsStore.createIndex(
+    DbTargetDocument.documentTargetsIndex,
+    DbTargetDocument.documentTargetsKeyPath,
+    { unique: true }
+  );
+
+  const targetStore = db.createObjectStore(DbTarget.store, {
+    keyPath: DbTarget.keyPath
+  });
+
+  // NOTE: This is unique only because the TargetId is the suffix.
+  targetStore.createIndex(
+    DbTarget.queryTargetsIndexName,
+    DbTarget.queryTargetsKeyPath,
+    { unique: true }
+  );
+  db.createObjectStore(DbTargetGlobal.store);
+}
+
+/**
+ * An object representing the changes at a particular snapshot version for the
+ * given target. This is used to facilitate storing query changelogs in the
+ * targetChanges object store.
+ *
+ * PORTING NOTE: This is used for change propagation during multi-tab syncing
+ * and not needed on iOS and Android.
+ */
+export class DbTargetChange {
+  /** Name of the IndexedDb object store.  */
+  static store = 'targetChanges';
+
+  /** Keys are automatically assigned via the targetId and snapshotVersion. */
+  static keyPath = ['targetId', 'snapshotVersion'];
+
+  constructor(
+    /**
+     * The targetId identifying a target.
+     */
+    public targetId: TargetId,
+    /**
+     * The snapshot version for this change.
+     */
+    public snapshotVersion: DbTimestamp,
+    /**
+     * The keys of the changed documents in this snapshot.
+     */
+    public changes: {
+      added?: EncodedResourcePath[];
+      modified?: EncodedResourcePath[];
+      removed?: EncodedResourcePath[];
+    }
+  ) {}
+}
+
+function createTargetChangeStore(db: IDBDatabase): void {
+  db.createObjectStore(DbTargetChange.store, {
+    keyPath: DbTargetChange.keyPath as KeyPath
+  });
+}
+
 /**
- * The list of all IndexedDB stored used by the SDK. This is used when creating
- * transactions so that access across all stores is done atomically.
+ * A record of the metadata state of each client.
+ *
+ * PORTING NOTE: This is used to synchronize multi-tab state and does not need
+ * to be ported to iOS or Android.
  */
-export const ALL_STORES = [
+export class DbClientMetadata {
+  /** Name of the IndexedDb object store. */
+  static store = 'clientMetadata';
+
+  /** Keys are automatically assigned via the clientKey properties. */
+  static keyPath = ['clientKey'];
+
+  constructor(
+    /** The auto-generated client key assigned at client startup. */
+    public clientKey: string,
+    /** The last time this state was updated. */
+    public updateTimeMs: DbTimestamp,
+    /** Whether this client is running in a foreground tab. */
+    public inForeground: boolean
+  ) {}
+}
+
+function createClientMetadataStore(db: IDBDatabase): void {
+  db.createObjectStore(DbClientMetadata.store, {
+    keyPath: DbClientMetadata.keyPath as KeyPath
+  });
+}
+
+// Visible for testing
+export const V1_STORES = [
   DbMutationQueue.store,
   DbMutationBatch.store,
   DbDocumentMutation.store,
@@ -469,3 +574,12 @@ export const ALL_STORES = [
   DbTargetGlobal.store,
   DbTargetDocument.store
 ];
+
+const V2_STORES = [DbClientMetadata.store, DbTargetChange.store];
+
+/**
+ * The list of all default IndexedDB stores used throughout the SDK. This is
+ * used when creating transactions so that access across all stores is done
+ * atomically.
+ */
+export const ALL_STORES = [...V1_STORES, ...V2_STORES];
diff --git a/packages/firestore/src/local/simple_db.ts b/packages/firestore/src/local/simple_db.ts
index cfaa6bb9767..8adbcad37d5 100644
--- a/packages/firestore/src/local/simple_db.ts
+++ b/packages/firestore/src/local/simple_db.ts
@@ -19,6 +19,7 @@ import { debug } from '../util/log';
 import { AnyDuringMigration } from '../util/misc';
 
 import { PersistencePromise } from './persistence_promise';
+import { SCHEMA_VERSION } from './indexeddb_schema';
 
 const LOG_TAG = 'SimpleDb';
 
@@ -34,7 +35,11 @@ export class SimpleDb {
   static openOrCreate(
     name: string,
     version: number,
-    runUpgrade: (db: IDBDatabase, oldVersion: number) => void
+    runUpgrade: (
+      db: IDBDatabase,
+      fromVersion: number,
+      toVersion: number
+    ) => void
   ): Promise<SimpleDb> {
     assert(
       SimpleDb.isAvailable(),
@@ -70,7 +75,7 @@ export class SimpleDb {
         // cheating and just passing the raw IndexedDB in, since
         // createObjectStore(), etc. are synchronous.
         const db = (event.target as IDBOpenDBRequest).result;
-        runUpgrade(db, event.oldVersion);
+        runUpgrade(db, event.oldVersion, SCHEMA_VERSION);
       };
     }).toPromise();
   }
diff --git a/packages/firestore/test/unit/local/schema_migration.test.ts b/packages/firestore/test/unit/local/schema_migration.test.ts
new file mode 100644
index 00000000000..3faad875333
--- /dev/null
+++ b/packages/firestore/test/unit/local/schema_migration.test.ts
@@ -0,0 +1,90 @@
+/**
+ * Copyright 2018 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.
+ */
+
+import { expect } from 'chai';
+import { IndexedDbPersistence } from '../../../src/local/indexeddb_persistence';
+import {
+  ALL_STORES,
+  createOrUpgradeDb,
+  V1_STORES
+} from '../../../src/local/indexeddb_schema';
+import { Deferred } from '../../../src/util/promise';
+import { SimpleDb } from '../../../src/local/simple_db';
+
+const INDEXEDDB_TEST_DATABASE = 'schemaTest';
+
+function withDb(schemaVersion, fn: (db: IDBDatabase) => void): Promise<void> {
+  return new Promise<IDBDatabase>((resolve, reject) => {
+    const request = window.indexedDB.open(
+      INDEXEDDB_TEST_DATABASE,
+      schemaVersion
+    );
+    request.onupgradeneeded = (event: IDBVersionChangeEvent) => {
+      const db = (event.target as IDBOpenDBRequest).result;
+      createOrUpgradeDb(db, event.oldVersion, schemaVersion);
+    };
+    request.onsuccess = (event: Event) => {
+      resolve((event.target as IDBOpenDBRequest).result);
+    };
+    request.onerror = (event: ErrorEvent) => {
+      reject((event.target as IDBOpenDBRequest).error);
+    };
+  }).then(db => {
+    fn(db);
+    db.close();
+  });
+}
+
+function getAllObjectStores(db: IDBDatabase): String[] {
+  const objectStores: String[] = [];
+  for (let i = 0; i < db.objectStoreNames.length; ++i) {
+    objectStores.push(db.objectStoreNames.item(i));
+  }
+  objectStores.sort();
+  return objectStores;
+}
+
+describe('IndexedDbSchema: createOrUpgradeDb', () => {
+  if (!IndexedDbPersistence.isAvailable()) {
+    console.warn('No IndexedDB. Skipping createOrUpgradeDb() tests.');
+    return;
+  }
+
+  beforeEach(() => SimpleDb.delete(INDEXEDDB_TEST_DATABASE));
+
+  it('can install schema version 1', () => {
+    return withDb(1, db => {
+      expect(db.version).to.be.equal(1);
+      expect(getAllObjectStores(db)).to.have.members(V1_STORES);
+    });
+  });
+
+  it('can install schema version 2', () => {
+    return withDb(2, db => {
+      expect(db.version).to.be.equal(2);
+      expect(getAllObjectStores(db)).to.have.members(ALL_STORES);
+    });
+  });
+
+  it('can upgrade from schema version 1 to 2', () => {
+    return withDb(1, () => {}).then(() =>
+      withDb(2, db => {
+        expect(db.version).to.be.equal(2);
+        expect(getAllObjectStores(db)).to.have.members(ALL_STORES);
+      })
+    );
+  });
+});