This book constitutes the refereed proceedings of the 17th International Symposium on Formal Methods, FM 2011, held in Limerick, Ireland, in June 2011.The 29 revised full papers presented together with 3 invited talks were carefully reviewed and selected from numerous submissions. The papers are organized in topical sections on cyber-physical systems, runtime analysis, case studies/tools, experience, program compilation and transformation, security, progress algebra, education, concurrency, dynamic structures, and model checking.