This book constitutes the refereed proceedings of the 9th International Conference on Reliable Software Technologies, Ada-Europe 2004, held in Palma de Mallorca, Spain in June 2004.The 23 revised full papers presented together with 3 invited papers were carefully reviewed and selected from numerous submissions. The papers are organized in topical sections on static analysis, distributed systems, real-time systems, reflection and XML, testing, critical systems modeling, scheduling, and application programming interfaces.