In Flutter, the runApp() and main() functions are essential for building and running applications. The main() function is the entry point of every Dart application, including Flutter applications. In a Flutter application, the main() function typically calls the runApp() function, which initializes the Flutter framework and runs the application. The runApp() function is responsible for creating a Flutter App widget and attaching it to the device screen. This function takes an argument of a Widget object that represents the root of the application's widget tree. The Widget object is usually an instance of the MaterialApp or CupertinoApp widget, which are pre-built widgets that provide common design patterns for Material Design and Cupertino (iOS) style apps respectively. Here is an example of how main() and runApp() functions are used in a Flutter application: In the above example, the main() function calls the runApp() function with an instance of the MyApp widget as an argument. The MyApp widget is defined as a stateless widget that returns a MaterialApp widget as its child. The MaterialApp widget provides a basic Material Design scaffold that displays a title bar and a centered text widget that displays the text "Hello, World!".