This book constitutes the refereed proceedings of the 15th International Symposium on Methodologies for Intelligent Systems, ISMIS 2005, held in Saratoga Springs, NY, USA in May 2005. The 69 revised full papers presented together with 2 invited papers were carefully reviewed and selected from close to 200 submissions. The papers are organized in topical sections on knowledge discovery and data mining, intelligent information systems, information and knowledge integration, soft computing, clustering, Web data processing, AI logics, applications, intelligent information retrieval, and knowledge representation.