This Book Constitutes The Refereed Proceedings Of The 13th International Conference On Conceptual Structures, Iccs 2005, Held In Kassel, Germany, In July 2005. The 23 Revised Full Papers Presented Together With 9 Invited Papers Were Carefully Reviewed And Selected From 66 Submissions. The Papers Are Organized In Topical Sections On Theoretical Foundations, Knowledge Engineering And Tools, And Knowledge Acquisition And Ontologies.