. If you want the same app to run on older versions of Android, this is possible by specifying a lower version number for the min SDK. But now you have to be prepared to handle any class differences that exist in stuff you're using in your app. The reason you might target a higher version than the min is that you might want to take advantage of a feature that exists in the higher version, while gracefully handling the case when a class or method doesn't exist in an older version.