Unlike on Windows, the convention on Mac is that when the main application Window is closed, the application does not exit (although there are exception to this). If you are working on a Document based application, the functionality to open a new window is built in (just open a new document), however for a non-Document based Cocoa application, you have to implement this functionality yourself, which is pretty simple. First, you have to tell the window (NSWindow) to only hide itself when it is closed, and not also release itself.