diff --git a/.changeset/hip-apricots-end.md b/.changeset/hip-apricots-end.md
new file mode 100644
index 00000000000..40bfedbaeec
--- /dev/null
+++ b/.changeset/hip-apricots-end.md
@@ -0,0 +1,7 @@
+---
+'@firebase/remote-config-types': minor
+'@firebase/remote-config': minor
+'firebase': minor
+---
+
+Added support for custom signal targeting in Remote Config. Use `setCustomSignals` API for setting custom signals and use them to build custom targeting conditions in Remote Config.
diff --git a/common/api-review/remote-config.api.md b/common/api-review/remote-config.api.md
index 980d8f3d287..bf6cf4761de 100644
--- a/common/api-review/remote-config.api.md
+++ b/common/api-review/remote-config.api.md
@@ -9,6 +9,12 @@ import { FirebaseApp } from '@firebase/app';
 // @public
 export function activate(remoteConfig: RemoteConfig): Promise<boolean>;
 
+// @public
+export interface CustomSignals {
+    // (undocumented)
+    [key: string]: string | number | null;
+}
+
 // @public
 export function ensureInitialized(remoteConfig: RemoteConfig): Promise<void>;
 
@@ -62,6 +68,9 @@ export interface RemoteConfigSettings {
     minimumFetchIntervalMillis: number;
 }
 
+// @public
+export function setCustomSignals(remoteConfig: RemoteConfig, customSignals: CustomSignals): Promise<void>;
+
 // @public
 export function setLogLevel(remoteConfig: RemoteConfig, logLevel: LogLevel): void;
 
diff --git a/docs-devsite/_toc.yaml b/docs-devsite/_toc.yaml
index ca06d4f9398..4ab67bcd6ef 100644
--- a/docs-devsite/_toc.yaml
+++ b/docs-devsite/_toc.yaml
@@ -428,6 +428,8 @@ toc:
 - title: remote-config
   path: /docs/reference/js/remote-config.md
   section:
+  - title: CustomSignals
+    path: /docs/reference/js/remote-config.customsignals.md
   - title: RemoteConfig
     path: /docs/reference/js/remote-config.remoteconfig.md
   - title: RemoteConfigSettings
diff --git a/docs-devsite/remote-config.customsignals.md b/docs-devsite/remote-config.customsignals.md
new file mode 100644
index 00000000000..98bd371ad7b
--- /dev/null
+++ b/docs-devsite/remote-config.customsignals.md
@@ -0,0 +1,23 @@
+Project: /docs/reference/js/_project.yaml
+Book: /docs/reference/_book.yaml
+page_type: reference
+
+{% comment %}
+DO NOT EDIT THIS FILE!
+This is generated by the JS SDK team, and any local changes will be
+overwritten. Changes should be made in the source code at
+https://github.com/firebase/firebase-js-sdk
+{% endcomment %}
+
+# CustomSignals interface
+Defines the type for representing custom signals and their values.
+
+<p>The values in CustomSignals must be one of the following types:
+
+<ul> <li><code>string</code> <li><code>number</code> <li><code>null</code> </ul>
+
+<b>Signature:</b>
+
+```typescript
+export interface CustomSignals 
+```
diff --git a/docs-devsite/remote-config.md b/docs-devsite/remote-config.md
index 371ab7ff157..40319453a3f 100644
--- a/docs-devsite/remote-config.md
+++ b/docs-devsite/remote-config.md
@@ -28,6 +28,7 @@ The Firebase Remote Config Web SDK. This SDK does not work in a Node.js environm
 |  [getNumber(remoteConfig, key)](./remote-config.md#getnumber_476c09f) | Gets the value for the given key as a number.<!-- -->Convenience method for calling <code>remoteConfig.getValue(key).asNumber()</code>. |
 |  [getString(remoteConfig, key)](./remote-config.md#getstring_476c09f) | Gets the value for the given key as a string. Convenience method for calling <code>remoteConfig.getValue(key).asString()</code>. |
 |  [getValue(remoteConfig, key)](./remote-config.md#getvalue_476c09f) | Gets the [Value](./remote-config.value.md#value_interface) for the given key. |
+|  [setCustomSignals(remoteConfig, customSignals)](./remote-config.md#setcustomsignals_aeeb95e) | Sets the custom signals for the app instance. |
 |  [setLogLevel(remoteConfig, logLevel)](./remote-config.md#setloglevel_039a45b) | Defines the log level to use. |
 |  <b>function()</b> |
 |  [isSupported()](./remote-config.md#issupported) | This method provides two different checks:<!-- -->1. Check if IndexedDB exists in the browser environment. 2. Check if the current browser context allows IndexedDB <code>open()</code> calls. |
@@ -36,6 +37,7 @@ The Firebase Remote Config Web SDK. This SDK does not work in a Node.js environm
 
 |  Interface | Description |
 |  --- | --- |
+|  [CustomSignals](./remote-config.customsignals.md#customsignals_interface) | Defines the type for representing custom signals and their values.<p>The values in CustomSignals must be one of the following types:<ul> <li><code>string</code> <li><code>number</code> <li><code>null</code> </ul> |
 |  [RemoteConfig](./remote-config.remoteconfig.md#remoteconfig_interface) | The Firebase Remote Config service interface. |
 |  [RemoteConfigSettings](./remote-config.remoteconfigsettings.md#remoteconfigsettings_interface) | Defines configuration options for the Remote Config SDK. |
 |  [Value](./remote-config.value.md#value_interface) | Wraps a value with metadata and type-safe getters. |
@@ -276,6 +278,27 @@ export declare function getValue(remoteConfig: RemoteConfig, key: string): Value
 
 The value for the given key.
 
+### setCustomSignals(remoteConfig, customSignals) {:#setcustomsignals_aeeb95e}
+
+Sets the custom signals for the app instance.
+
+<b>Signature:</b>
+
+```typescript
+export declare function setCustomSignals(remoteConfig: RemoteConfig, customSignals: CustomSignals): Promise<void>;
+```
+
+#### Parameters
+
+|  Parameter | Type | Description |
+|  --- | --- | --- |
+|  remoteConfig | [RemoteConfig](./remote-config.remoteconfig.md#remoteconfig_interface) | The [RemoteConfig](./remote-config.remoteconfig.md#remoteconfig_interface) instance. |
+|  customSignals | [CustomSignals](./remote-config.customsignals.md#customsignals_interface) | Map (key, value) of the custom signals to be set for the app instance. If a key already exists, the value is overwritten. Setting the value of a custom signal to null unsets the signal. The signals will be persisted locally on the client. |
+
+<b>Returns:</b>
+
+Promise&lt;void&gt;
+
 ### setLogLevel(remoteConfig, logLevel) {:#setloglevel_039a45b}
 
 Defines the log level to use.
diff --git a/packages/firebase/compat/index.d.ts b/packages/firebase/compat/index.d.ts
index efda7c954a5..92c7bd2c278 100644
--- a/packages/firebase/compat/index.d.ts
+++ b/packages/firebase/compat/index.d.ts
@@ -2046,6 +2046,7 @@ declare namespace firebase.remoteConfig {
    * Defines levels of Remote Config logging.
    */
   export type LogLevel = 'debug' | 'error' | 'silent';
+
   /**
    * This method provides two different checks:
    *
diff --git a/packages/remote-config-types/index.d.ts b/packages/remote-config-types/index.d.ts
index a088f665310..7fbaf7c3e5c 100644
--- a/packages/remote-config-types/index.d.ts
+++ b/packages/remote-config-types/index.d.ts
@@ -173,6 +173,19 @@ export type FetchStatus = 'no-fetch-yet' | 'success' | 'failure' | 'throttle';
  */
 export type LogLevel = 'debug' | 'error' | 'silent';
 
+/**
+ * Defines the type for representing custom signals and their values.
+ *
+ * <p>The values in CustomSignals must be one of the following types:
+ *
+ * <ul>
+ *   <li><code>string</code>
+ *   <li><code>number</code>
+ *   <li><code>null</code>
+ * </ul>
+ */
+export type CustomSignals = { [key: string]: string | number | null };
+
 declare module '@firebase/component' {
   interface NameServiceMapping {
     'remoteConfig-compat': RemoteConfig;
diff --git a/packages/remote-config/src/api.ts b/packages/remote-config/src/api.ts
index aeae67d450e..607d4944d26 100644
--- a/packages/remote-config/src/api.ts
+++ b/packages/remote-config/src/api.ts
@@ -17,12 +17,17 @@
 
 import { _getProvider, FirebaseApp, getApp } from '@firebase/app';
 import {
+  CustomSignals,
   LogLevel as RemoteConfigLogLevel,
   RemoteConfig,
   Value
 } from './public_types';
 import { RemoteConfigAbortSignal } from './client/remote_config_fetch_client';
-import { RC_COMPONENT_NAME } from './constants';
+import {
+  RC_COMPONENT_NAME,
+  RC_CUSTOM_SIGNAL_KEY_MAX_LENGTH,
+  RC_CUSTOM_SIGNAL_VALUE_MAX_LENGTH
+} from './constants';
 import { ErrorCode, hasErrorCode } from './errors';
 import { RemoteConfig as RemoteConfigImpl } from './remote_config';
 import { Value as ValueImpl } from './value';
@@ -114,11 +119,18 @@ export async function fetchConfig(remoteConfig: RemoteConfig): Promise<void> {
     abortSignal.abort();
   }, rc.settings.fetchTimeoutMillis);
 
+  const customSignals = rc._storageCache.getCustomSignals();
+  if (customSignals) {
+    rc._logger.debug(
+      `Fetching config with custom signals: ${JSON.stringify(customSignals)}`
+    );
+  }
   // Catches *all* errors thrown by client so status can be set consistently.
   try {
     await rc._client.fetch({
       cacheMaxAgeMillis: rc.settings.minimumFetchIntervalMillis,
-      signal: abortSignal
+      signal: abortSignal,
+      customSignals
     });
 
     await rc._storageCache.setLastFetchStatus('success');
@@ -258,3 +270,51 @@ export function setLogLevel(
 function getAllKeys(obj1: {} = {}, obj2: {} = {}): string[] {
   return Object.keys({ ...obj1, ...obj2 });
 }
+
+/**
+ * Sets the custom signals for the app instance.
+ *
+ * @param remoteConfig - The {@link RemoteConfig} instance.
+ * @param customSignals - Map (key, value) of the custom signals to be set for the app instance. If
+ * a key already exists, the value is overwritten. Setting the value of a custom signal to null
+ * unsets the signal. The signals will be persisted locally on the client.
+ *
+ * @public
+ */
+export async function setCustomSignals(
+  remoteConfig: RemoteConfig,
+  customSignals: CustomSignals
+): Promise<void> {
+  const rc = getModularInstance(remoteConfig) as RemoteConfigImpl;
+  if (Object.keys(customSignals).length === 0) {
+    return;
+  }
+
+  // eslint-disable-next-line guard-for-in
+  for (const key in customSignals) {
+    if (key.length > RC_CUSTOM_SIGNAL_KEY_MAX_LENGTH) {
+      rc._logger.error(
+        `Custom signal key ${key} is too long, max allowed length is ${RC_CUSTOM_SIGNAL_KEY_MAX_LENGTH}.`
+      );
+      return;
+    }
+    const value = customSignals[key];
+    if (
+      typeof value === 'string' &&
+      value.length > RC_CUSTOM_SIGNAL_VALUE_MAX_LENGTH
+    ) {
+      rc._logger.error(
+        `Value supplied for custom signal ${key} is too long, max allowed length is ${RC_CUSTOM_SIGNAL_VALUE_MAX_LENGTH}.`
+      );
+      return;
+    }
+  }
+
+  try {
+    await rc._storageCache.setCustomSignals(customSignals);
+  } catch (error) {
+    rc._logger.error(
+      `Error encountered while setting custom signals: ${error}`
+    );
+  }
+}
diff --git a/packages/remote-config/src/client/remote_config_fetch_client.ts b/packages/remote-config/src/client/remote_config_fetch_client.ts
index 25e00299855..71ea66d5e50 100644
--- a/packages/remote-config/src/client/remote_config_fetch_client.ts
+++ b/packages/remote-config/src/client/remote_config_fetch_client.ts
@@ -15,6 +15,8 @@
  * limitations under the License.
  */
 
+import { CustomSignals } from '../public_types';
+
 /**
  * Defines a client, as in https://en.wikipedia.org/wiki/Client%E2%80%93server_model, for the
  * Remote Config server (https://firebase.google.com/docs/reference/remote-config/rest).
@@ -99,6 +101,12 @@ export interface FetchRequest {
    * <p>Comparable to passing `headers = { 'If-None-Match': <eTag> }` to the native Fetch API.
    */
   eTag?: string;
+
+  /** The custom signals stored for the app instance.
+   *
+   * <p>Optional in case no custom signals are set for the instance.
+   */
+  customSignals?: CustomSignals;
 }
 
 /**
diff --git a/packages/remote-config/src/client/rest_client.ts b/packages/remote-config/src/client/rest_client.ts
index 87fdae3c3d6..9d87ffbb1ac 100644
--- a/packages/remote-config/src/client/rest_client.ts
+++ b/packages/remote-config/src/client/rest_client.ts
@@ -15,6 +15,7 @@
  * limitations under the License.
  */
 
+import { CustomSignals } from '../public_types';
 import {
   FetchResponse,
   RemoteConfigFetchClient,
@@ -41,6 +42,7 @@ interface FetchRequestBody {
   app_instance_id_token: string;
   app_id: string;
   language_code: string;
+  custom_signals?: CustomSignals;
   /* eslint-enable camelcase */
 }
 
@@ -92,7 +94,8 @@ export class RestClient implements RemoteConfigFetchClient {
       app_instance_id: installationId,
       app_instance_id_token: installationToken,
       app_id: this.appId,
-      language_code: getUserLanguage()
+      language_code: getUserLanguage(),
+      custom_signals: request.customSignals
       /* eslint-enable camelcase */
     };
 
diff --git a/packages/remote-config/src/constants.ts b/packages/remote-config/src/constants.ts
index 365d9037f86..d7d286909a5 100644
--- a/packages/remote-config/src/constants.ts
+++ b/packages/remote-config/src/constants.ts
@@ -16,3 +16,6 @@
  */
 
 export const RC_COMPONENT_NAME = 'remote-config';
+export const RC_CUSTOM_SIGNAL_MAX_ALLOWED_SIGNALS = 100;
+export const RC_CUSTOM_SIGNAL_KEY_MAX_LENGTH = 250;
+export const RC_CUSTOM_SIGNAL_VALUE_MAX_LENGTH = 500;
diff --git a/packages/remote-config/src/errors.ts b/packages/remote-config/src/errors.ts
index eac9a25657b..762eeb899ee 100644
--- a/packages/remote-config/src/errors.ts
+++ b/packages/remote-config/src/errors.ts
@@ -31,7 +31,8 @@ export const enum ErrorCode {
   FETCH_THROTTLE = 'fetch-throttle',
   FETCH_PARSE = 'fetch-client-parse',
   FETCH_STATUS = 'fetch-status',
-  INDEXED_DB_UNAVAILABLE = 'indexed-db-unavailable'
+  INDEXED_DB_UNAVAILABLE = 'indexed-db-unavailable',
+  CUSTOM_SIGNAL_MAX_ALLOWED_SIGNALS = 'custom-signal-max-allowed-signals'
 }
 
 const ERROR_DESCRIPTION_MAP: { readonly [key in ErrorCode]: string } = {
@@ -67,7 +68,9 @@ const ERROR_DESCRIPTION_MAP: { readonly [key in ErrorCode]: string } = {
   [ErrorCode.FETCH_STATUS]:
     'Fetch server returned an HTTP error status. HTTP status: {$httpStatus}.',
   [ErrorCode.INDEXED_DB_UNAVAILABLE]:
-    'Indexed DB is not supported by current browser'
+    'Indexed DB is not supported by current browser',
+  [ErrorCode.CUSTOM_SIGNAL_MAX_ALLOWED_SIGNALS]:
+    'Setting more than {$maxSignals} custom signals is not supported.'
 };
 
 // Note this is effectively a type system binding a code to params. This approach overlaps with the
@@ -86,6 +89,7 @@ interface ErrorParams {
   [ErrorCode.FETCH_THROTTLE]: { throttleEndTimeMillis: number };
   [ErrorCode.FETCH_PARSE]: { originalErrorMessage: string };
   [ErrorCode.FETCH_STATUS]: { httpStatus: number };
+  [ErrorCode.CUSTOM_SIGNAL_MAX_ALLOWED_SIGNALS]: { maxSignals: number };
 }
 
 export const ERROR_FACTORY = new ErrorFactory<ErrorCode, ErrorParams>(
diff --git a/packages/remote-config/src/public_types.ts b/packages/remote-config/src/public_types.ts
index d489809e451..365d5e5905f 100644
--- a/packages/remote-config/src/public_types.ts
+++ b/packages/remote-config/src/public_types.ts
@@ -134,6 +134,23 @@ export type FetchStatus = 'no-fetch-yet' | 'success' | 'failure' | 'throttle';
  */
 export type LogLevel = 'debug' | 'error' | 'silent';
 
+/**
+ * Defines the type for representing custom signals and their values.
+ *
+ * <p>The values in CustomSignals must be one of the following types:
+ *
+ * <ul>
+ *   <li><code>string</code>
+ *   <li><code>number</code>
+ *   <li><code>null</code>
+ * </ul>
+ *
+ * @public
+ */
+export interface CustomSignals {
+  [key: string]: string | number | null;
+}
+
 declare module '@firebase/component' {
   interface NameServiceMapping {
     'remote-config': RemoteConfig;
diff --git a/packages/remote-config/src/storage/storage.ts b/packages/remote-config/src/storage/storage.ts
index baa7ab46b52..52e660f1fdb 100644
--- a/packages/remote-config/src/storage/storage.ts
+++ b/packages/remote-config/src/storage/storage.ts
@@ -15,12 +15,13 @@
  * limitations under the License.
  */
 
-import { FetchStatus } from '@firebase/remote-config-types';
+import { FetchStatus, CustomSignals } from '@firebase/remote-config-types';
 import {
   FetchResponse,
   FirebaseRemoteConfigObject
 } from '../client/remote_config_fetch_client';
 import { ERROR_FACTORY, ErrorCode } from '../errors';
+import { RC_CUSTOM_SIGNAL_MAX_ALLOWED_SIGNALS } from '../constants';
 import { FirebaseError } from '@firebase/util';
 
 /**
@@ -70,7 +71,8 @@ type ProjectNamespaceKeyFieldValue =
   | 'last_successful_fetch_timestamp_millis'
   | 'last_successful_fetch_response'
   | 'settings'
-  | 'throttle_metadata';
+  | 'throttle_metadata'
+  | 'custom_signals';
 
 // Visible for testing.
 export function openDatabase(): Promise<IDBDatabase> {
@@ -181,10 +183,64 @@ export class Storage {
     return this.delete('throttle_metadata');
   }
 
-  async get<T>(key: ProjectNamespaceKeyFieldValue): Promise<T | undefined> {
+  getCustomSignals(): Promise<CustomSignals | undefined> {
+    return this.get<CustomSignals>('custom_signals');
+  }
+
+  async setCustomSignals(customSignals: CustomSignals): Promise<CustomSignals> {
     const db = await this.openDbPromise;
+    const transaction = db.transaction([APP_NAMESPACE_STORE], 'readwrite');
+    const storedSignals = await this.getWithTransaction<CustomSignals>(
+      'custom_signals',
+      transaction
+    );
+    const combinedSignals = {
+      ...storedSignals,
+      ...customSignals
+    };
+    // Filter out key-value assignments with null values since they are signals being unset
+    const updatedSignals = Object.fromEntries(
+      Object.entries(combinedSignals)
+        .filter(([_, v]) => v !== null)
+        .map(([k, v]) => {
+          // Stringify numbers to store a map of string keys and values which can be sent
+          // as-is in a fetch call.
+          if (typeof v === 'number') {
+            return [k, v.toString()];
+          }
+          return [k, v];
+        })
+    );
+
+    // Throw an error if the number of custom signals to be stored exceeds the limit
+    if (
+      Object.keys(updatedSignals).length > RC_CUSTOM_SIGNAL_MAX_ALLOWED_SIGNALS
+    ) {
+      throw ERROR_FACTORY.create(ErrorCode.CUSTOM_SIGNAL_MAX_ALLOWED_SIGNALS, {
+        maxSignals: RC_CUSTOM_SIGNAL_MAX_ALLOWED_SIGNALS
+      });
+    }
+
+    await this.setWithTransaction<CustomSignals>(
+      'custom_signals',
+      updatedSignals,
+      transaction
+    );
+    return updatedSignals;
+  }
+
+  /**
+   * Gets a value from the database using the provided transaction.
+   *
+   * @param key The key of the value to get.
+   * @param transaction The transaction to use for the operation.
+   * @returns The value associated with the key, or undefined if no such value exists.
+   */
+  async getWithTransaction<T>(
+    key: ProjectNamespaceKeyFieldValue,
+    transaction: IDBTransaction
+  ): Promise<T | undefined> {
     return new Promise((resolve, reject) => {
-      const transaction = db.transaction([APP_NAMESPACE_STORE], 'readonly');
       const objectStore = transaction.objectStore(APP_NAMESPACE_STORE);
       const compositeKey = this.createCompositeKey(key);
       try {
@@ -210,10 +266,20 @@ export class Storage {
     });
   }
 
-  async set<T>(key: ProjectNamespaceKeyFieldValue, value: T): Promise<void> {
-    const db = await this.openDbPromise;
+  /**
+   * Sets a value in the database using the provided transaction.
+   *
+   * @param key The key of the value to set.
+   * @param value The value to set.
+   * @param transaction The transaction to use for the operation.
+   * @returns A promise that resolves when the operation is complete.
+   */
+  async setWithTransaction<T>(
+    key: ProjectNamespaceKeyFieldValue,
+    value: T,
+    transaction: IDBTransaction
+  ): Promise<void> {
     return new Promise((resolve, reject) => {
-      const transaction = db.transaction([APP_NAMESPACE_STORE], 'readwrite');
       const objectStore = transaction.objectStore(APP_NAMESPACE_STORE);
       const compositeKey = this.createCompositeKey(key);
       try {
@@ -237,6 +303,18 @@ export class Storage {
     });
   }
 
+  async get<T>(key: ProjectNamespaceKeyFieldValue): Promise<T | undefined> {
+    const db = await this.openDbPromise;
+    const transaction = db.transaction([APP_NAMESPACE_STORE], 'readonly');
+    return this.getWithTransaction<T>(key, transaction);
+  }
+
+  async set<T>(key: ProjectNamespaceKeyFieldValue, value: T): Promise<void> {
+    const db = await this.openDbPromise;
+    const transaction = db.transaction([APP_NAMESPACE_STORE], 'readwrite');
+    return this.setWithTransaction<T>(key, value, transaction);
+  }
+
   async delete(key: ProjectNamespaceKeyFieldValue): Promise<void> {
     const db = await this.openDbPromise;
     return new Promise((resolve, reject) => {
diff --git a/packages/remote-config/src/storage/storage_cache.ts b/packages/remote-config/src/storage/storage_cache.ts
index 302ba9a2487..fc419b0068e 100644
--- a/packages/remote-config/src/storage/storage_cache.ts
+++ b/packages/remote-config/src/storage/storage_cache.ts
@@ -15,7 +15,7 @@
  * limitations under the License.
  */
 
-import { FetchStatus } from '@firebase/remote-config-types';
+import { FetchStatus, CustomSignals } from '@firebase/remote-config-types';
 import { FirebaseRemoteConfigObject } from '../client/remote_config_fetch_client';
 import { Storage } from './storage';
 
@@ -31,6 +31,7 @@ export class StorageCache {
   private lastFetchStatus?: FetchStatus;
   private lastSuccessfulFetchTimestampMillis?: number;
   private activeConfig?: FirebaseRemoteConfigObject;
+  private customSignals?: CustomSignals;
 
   /**
    * Memory-only getters
@@ -47,6 +48,10 @@ export class StorageCache {
     return this.activeConfig;
   }
 
+  getCustomSignals(): CustomSignals | undefined {
+    return this.customSignals;
+  }
+
   /**
    * Read-ahead getter
    */
@@ -55,6 +60,7 @@ export class StorageCache {
     const lastSuccessfulFetchTimestampMillisPromise =
       this.storage.getLastSuccessfulFetchTimestampMillis();
     const activeConfigPromise = this.storage.getActiveConfig();
+    const customSignalsPromise = this.storage.getCustomSignals();
 
     // Note:
     // 1. we consistently check for undefined to avoid clobbering defined values
@@ -78,6 +84,11 @@ export class StorageCache {
     if (activeConfig) {
       this.activeConfig = activeConfig;
     }
+
+    const customSignals = await customSignalsPromise;
+    if (customSignals) {
+      this.customSignals = customSignals;
+    }
   }
 
   /**
@@ -99,4 +110,8 @@ export class StorageCache {
     this.activeConfig = activeConfig;
     return this.storage.setActiveConfig(activeConfig);
   }
+
+  async setCustomSignals(customSignals: CustomSignals): Promise<void> {
+    this.customSignals = await this.storage.setCustomSignals(customSignals);
+  }
 }
diff --git a/packages/remote-config/test/remote_config.test.ts b/packages/remote-config/test/remote_config.test.ts
index f53f4a72c86..51304bc3b2f 100644
--- a/packages/remote-config/test/remote_config.test.ts
+++ b/packages/remote-config/test/remote_config.test.ts
@@ -42,7 +42,8 @@ import {
   getString,
   getValue,
   setLogLevel,
-  fetchConfig
+  fetchConfig,
+  setCustomSignals
 } from '../src/api';
 import * as api from '../src/api';
 import { fetchAndActivate } from '../src';
@@ -93,6 +94,48 @@ describe('RemoteConfig', () => {
     loggerLogLevelSpy.restore();
   });
 
+  describe('setCustomSignals', () => {
+    beforeEach(() => {
+      storageCache.setCustomSignals = sinon.stub();
+      storage.setCustomSignals = sinon.stub();
+      logger.error = sinon.stub();
+    });
+
+    it('call storage API to store signals', async () => {
+      await setCustomSignals(rc, { key: 'value' });
+
+      expect(storageCache.setCustomSignals).to.have.been.calledWith({
+        key: 'value'
+      });
+    });
+
+    it('logs an error when supplied with a custom signal key greater than 250 characters', async () => {
+      const longKey = 'a'.repeat(251);
+      const customSignals = { [longKey]: 'value' };
+
+      await setCustomSignals(rc, customSignals);
+
+      expect(storageCache.setCustomSignals).to.not.have.been.called;
+      expect(logger.error).to.have.been.called;
+    });
+
+    it('logs an error when supplied with a custom signal value greater than 500 characters', async () => {
+      const longValue = 'a'.repeat(501);
+      const customSignals = { 'key': longValue };
+
+      await setCustomSignals(rc, customSignals);
+
+      expect(storageCache.setCustomSignals).to.not.have.been.called;
+      expect(logger.error).to.have.been.called;
+    });
+
+    it('empty custom signals map does nothing', async () => {
+      await setCustomSignals(rc, {});
+
+      expect(storageCache.setCustomSignals).to.not.have.been.called;
+    });
+  });
+
   // Adapts getUserLanguage tests from packages/auth/test/utils_test.js for TypeScript.
   describe('setLogLevel', () => {
     it('proxies to the FirebaseLogger instance', () => {
@@ -449,6 +492,7 @@ describe('RemoteConfig', () => {
         .stub()
         .returns(Promise.resolve({ status: 200 } as FetchResponse));
       storageCache.setLastFetchStatus = sinon.stub();
+      storageCache.getCustomSignals = sinon.stub();
       timeoutStub = sinon.stub(window, 'setTimeout');
     });
 
@@ -517,5 +561,11 @@ describe('RemoteConfig', () => {
         'failure'
       );
     });
+
+    it('sends custom signals', async () => {
+      await fetchConfig(rc);
+
+      expect(storageCache.getCustomSignals).to.have.been.called;
+    });
   });
 });
diff --git a/packages/remote-config/test/storage/storage.test.ts b/packages/remote-config/test/storage/storage.test.ts
index 92cc12225e8..7a865107791 100644
--- a/packages/remote-config/test/storage/storage.test.ts
+++ b/packages/remote-config/test/storage/storage.test.ts
@@ -117,4 +117,58 @@ describe('Storage', () => {
 
     expect(actualMetadata).to.be.undefined;
   });
+
+  it('sets and gets custom signals', async () => {
+    const customSignals = { key: 'value', key1: 'value1', key2: 1 };
+    const customSignalsInStorage = {
+      key: 'value',
+      key1: 'value1',
+      key2: '1'
+    };
+
+    await storage.setCustomSignals(customSignals);
+
+    const storedCustomSignals = await storage.getCustomSignals();
+
+    expect(storedCustomSignals).to.deep.eq(customSignalsInStorage);
+  });
+
+  it('upserts custom signals when key is present in storage', async () => {
+    const customSignals = { key: 'value', key1: 'value1' };
+    const updatedSignals = { key: 'value', key1: 'value2' };
+
+    await storage.setCustomSignals(customSignals);
+
+    await storage.setCustomSignals({ key1: 'value2' });
+
+    const storedCustomSignals = await storage.getCustomSignals();
+
+    expect(storedCustomSignals).to.deep.eq(updatedSignals);
+  });
+
+  it('deletes custom signal when value supplied is null', async () => {
+    const customSignals = { key: 'value', key1: 'value1' };
+    const updatedSignals = { key: 'value' };
+
+    await storage.setCustomSignals(customSignals);
+
+    await storage.setCustomSignals({ key1: null });
+
+    const storedCustomSignals = await storage.getCustomSignals();
+
+    expect(storedCustomSignals).to.deep.eq(updatedSignals);
+  });
+
+  it('throws an error when supplied with excess custom signals', async () => {
+    const customSignals: { [key: string]: string } = {};
+    for (let i = 0; i < 101; i++) {
+      customSignals[`key${i}`] = `value${i}`;
+    }
+
+    await expect(
+      storage.setCustomSignals(customSignals)
+    ).to.eventually.be.rejectedWith(
+      'Remote Config: Setting more than 100 custom signals is not supported.'
+    );
+  });
 });
diff --git a/packages/remote-config/test/storage/storage_cache.test.ts b/packages/remote-config/test/storage/storage_cache.test.ts
index e7cfb0ef0da..8d11cfac46a 100644
--- a/packages/remote-config/test/storage/storage_cache.test.ts
+++ b/packages/remote-config/test/storage/storage_cache.test.ts
@@ -37,6 +37,7 @@ describe('StorageCache', () => {
       const status = 'success';
       const lastSuccessfulFetchTimestampMillis = 123;
       const activeConfig = { key: 'value' };
+      const customSignals = { 'key': 'value' };
 
       storage.getLastFetchStatus = sinon
         .stub()
@@ -47,12 +48,16 @@ describe('StorageCache', () => {
       storage.getActiveConfig = sinon
         .stub()
         .returns(Promise.resolve(activeConfig));
+      storage.getCustomSignals = sinon
+        .stub()
+        .returns(Promise.resolve(customSignals));
 
       await storageCache.loadFromStorage();
 
       expect(storage.getLastFetchStatus).to.have.been.called;
       expect(storage.getLastSuccessfulFetchTimestampMillis).to.have.been.called;
       expect(storage.getActiveConfig).to.have.been.called;
+      expect(storage.getCustomSignals).to.have.been.called;
 
       expect(storageCache.getLastFetchStatus()).to.eq(status);
       expect(storageCache.getLastSuccessfulFetchTimestampMillis()).to.deep.eq(
@@ -81,4 +86,26 @@ describe('StorageCache', () => {
       expect(storage.setActiveConfig).to.have.been.calledWith(activeConfig);
     });
   });
+
+  describe('setCustomSignals', () => {
+    const customSignals = { key: 'value' };
+
+    beforeEach(() => {
+      storage.setCustomSignals = sinon
+        .stub()
+        .returns(Promise.resolve(customSignals));
+    });
+
+    it('writes to memory cache', async () => {
+      await storageCache.setCustomSignals(customSignals);
+
+      expect(storageCache.getCustomSignals()).to.deep.eq(customSignals);
+    });
+
+    it('writes to persistent storage', async () => {
+      await storageCache.setCustomSignals(customSignals);
+
+      expect(storage.setCustomSignals).to.have.been.calledWith(customSignals);
+    });
+  });
 });