This book constitutes the refereed proceedings of the 23rd International Conference on Computer Safety, Reliability, and Security, SAFECOMP 2004, held in Potsdam, Germany, in September 2004. The 24 revised full papers presented together with abstracts of 3 invited presentations were carefully reviewed and selected from 63 submissions. The papers are organized in topical sections on safety cases, reliability , human factors, transportation, software development, fault tree analysis, formal methods and systems, security and quality of services, and hazard and risk analysis.