The main() function in Flutter is responsible for starting the program. Without the main() function, we cannot write any program in Flutter. The runApp function is responsible for returning the widgets attached to the screen as a root of the widget tree and will be rendered on the screen.  The main() function came from Java-like languages so it's where all the programs have started, without it, we can't write any program on Flutter even without the UI. The runApp() function should return a widget that would be attached to the screen as a root of the widget Tree that will be rendered on the screen. We know that Flutter is a Framework, whereas Dart is a language.   The main() function starts the execution of Dart Language, which in turn provides methods to load Flutter Components which is the runApp() method, which works as the main function for the Flutter Framework. In short, we can say that the main is the starting point of execution for Dart Language, and runApp() is the same for Flutter Framework.