This book constitutes the refereed proceedings of the 34th Annual German Conference on Artificial Intelligence, KI 2011, held in Berlin, Germany, in October 2011.The 32 revised full papers presented together with 3 invited talks were carefully reviewed and selected from 81 submissions. The papers are divided in topical sections on computational learning and datamining, knowledge representation and reasonings, augmented reality, swarm intelligence; and planning and scheduling.