Using and Asking: APIs Used in the Android Market and Asked About in StackOverflow David Kavaler, Daryl Posnett, Clint Gibler, Hao Chen, Premkumar Devanbu, and Vladimir Filkov Programming is knowledge intensive. While it is well understood that programmers spend lots of time looking for information, with few exceptions, there is a significant lack of data on what information they seek, and why. Modern platforms, like Android, comprise complex APIs that often perplex programmers. We ask: which elements are confusing, and why? Increasingly, when programmers need answers, they turn to StackOverflow. This provides a novel opportunity. There are a vast number of applications for Android devices, which can be readily analyzed, and many traces of interactions on StackOverflow. These provide a complementary perspective on using and asking, and allow the two phenomena to be studied together. How does the market demand for the USE of an API drive the market for knowledge about it? Here, we analyze data from Android applications and StackOverflow together, to find out what it is that programmers want to know and why.