What API function would I need to use in order to shutdown another application if I have a handle to that application's main window? Basically, I have an application that (upon startup) checks for a newer version of itself (on a network drive) and if it finds a newer version it launches another application to perform the file copy. This other application needs to terminate the calling app. Once the 'update' app launches, the first thing it does is get a handle to the calling app's main form, but now what do I do with it? I've tried DestroyWindow(), CloseWindow(), and even SendMessage (with the WM_CLOSE command) but for some reason, it doesn't seem to be closing correctly. Any ideas?