This book constitutes the refereed proceedings of the 6th International Conference on Reliable Software Technologies, Ada-Europe 2001, held in Leuven, Belgium, in May 2001.The 27 revised full papers presented together with five invited papers were carefully reviewed and selected from a large number of submissions. The papers are organized in topical sections on program analysis, distributed systems, real-time systems, language and patterns, dependable systems, APIs and components, real-time kernels, standard formats: UML and XML, and system evolution.