I'ma let him finish when his site comes up, but here why I generally recommend targeting Android 4:<p>1. If you want to make a UI that scales across all device sizes, and you don't want to use hacks like ActionBarSherlock that will become a maintenance headache after the moment of convenience, build your app skeleton around Android 4 APIs.<p>2. Targeting Android 4 avoids use of the Support Library for back-compatibility, and therefore avoids using FragmentActivity. This isn't as bad as some of the back-compatible action bar hacks, but it is still an unnecessary complication in most cases. N.B. you may still want to use the Support Library for new APIs like PagerAdapter.<p>3. Tablets are going to increase in importance, and for some apps, tablets are the main target. Center your implementation strategy around tablets as the ideal experience, with multiple fragments on each tablet-size layout that are "unrolled" into sub-activities when running on a handset.<p>4. If you think the above point implies a unified code-base, yes, it does. Targeting Android 4 and above will simplify your unified code base.<p>The exception is apps that MUST target every user, and every device in the field. For example, my consultancy had an engagement with a dating site that needed to upgrade their Android app. After weighing the pluses and minuses, the conclusion was that it was better to put in more effort and incur some technical debt to reach every possible user. On the other hand, if you are writing an enterprise app for a green-field deployment, don't even consider supporting old versions.