We are in the midst of a revolution in the study of extrasolar planets. Thousands of recent discoveries have revealed that planets are common — most stars host at least one — and they show much greater diversity in size and orbital architecture than is present in the Solar System. This wealth of discovery raises many questions. How does the diversity of planetary systems arise? What are the planets like today, and how have they changed over time? And finally, do any other planets host life? These questions are the focus of the APEx Department (Atmospheric Physics of Exoplanets) at the Max Planck Institute for Astronomy.