This book constitutes the thoroughly refereed and extended post-proceedings of the joint European Web Mining Forum, EWMF 2005, and the International Workshop on Knowledge Discovery and Ontologies, KDO 2005, held in association with ECML/PKDD in Porto, Portugal in October 2005.

The 10 revised full papers presented together with 1 invited paper and 1 particularly fitting contribution from KDO 2004 were carefully selected for inclusion in the book. The authors' revisions have been significantly improved by the reviewers' comments and the discussions following the presentation. The papers focus on sophisticated techniques and tools that are used for semantic reasoning, semantic Web research, and Web data mining.