This book constitutes the refereed proceedings of the 20th International Conference on Computer Safety, Reliability, and Security, SAFECOMP 2001, held in Budapest, Hungary, in September 2001. The 20 revised full papers presented together with three invited papers were carefully reviewed and selected. The book offers topical sections on reliability assessment and security, safety case and safety analysis, medical systems, human-machine interface, COTS - components off the shelf, testing, formal methods, and control systems.