Answer - App.xaml is a file used by Silverlight applications to declare shared resources like brushes, various style objects, templates etc. Also, the code-behind file of app.xaml.cs is used to handle global application level events like Application_Startup, Application_Exit, and Application_UnhandledException (similar to the Global.asax file for ASP.NET applications). When Visual Studio creates the app.xaml file automatically, it creates a few event handlers with some default code. You can change the code appropriately. Collapse private void Application_Startup(object sender, StartupEventArgs e) { } private void Application_Exit(object sender, EventArgs e) { } private void Application_UnhandledException(object sender, ApplicationUnhandledExceptionEventArgs e) { } For ASP.NET developers, the above code will look familiar. This is similar to the application level event handlers in Global.asax.