This book constitutes the refereed proceedings of the 11th International Conference on Database Theory, ICDT 2007, held in Spain in January 2007. The papers are organized in topical sections on information integration and peer to peer, axiomatizations for XML, expressive power of query languages, incompleteness, inconsistency, and uncertainty, XML schemas and typechecking, stream processing and sequential query processing, ranking, XML update and query, as well as query containment.