This book constitutes the refereed proceedings of the 21st Annual German Conference on Artificial Intelligence, KI-97, held in Freiburg, Germany, in September 1997. The volume presents revised versions of 26 full papers and 10 posters selected from around 70 submissions from more than 15 countries. Also included are three excellent invited contributions by Anthony G. Cohn, Kurt Konolige, and Pat Langley. The papers are organized in topical sections on theorem proving, nonclassical logics, knowledge representation, spatial reasoning, computational linguistics, computer perception and neural nets, and on planning, diagnosis and search.