[Home](./index.md) > [@firebase/app](./app.md) > [initializeApp](./app.initializeapp_1.md) ## initializeApp() function Creates and initializes a FirebaseApp instance. Signature: ```typescript export declare function initializeApp(options: FirebaseOptions, config?: FirebaseAppConfig): FirebaseApp; ``` ## Parameters | Parameter | Type | Description | | --- | --- | --- | | options | [FirebaseOptions](./app.firebaseoptions.md) | Options to configure the app's services. | | config | [FirebaseAppConfig](./app.firebaseappconfig.md) | FirebaseApp Configuration | Returns: [FirebaseApp](./app.firebaseapp.md)