This book constitutes the refereed proceedings of the 42nd International Conference on Computer Safety, Reliability and Security, SAFECOMP 2023, which took place in Toulouse, France, in September 2023.The 20 full papers included in this volume were carefully reviewed and selected from 100 submissions. They were organized in topical sections as follows: Safety assurance; software testing and reliability; neural networks robustness and monitoring; model-based security and threat analysis; safety of autonomous driving; security engineering; AI safety; and neural networks and testing.