"25 at 25" contains articles from the last 25 years of the Safety Critical Systems Club (SCSC) newsletter Safety Systems. The club is for engineers, managers and academics in the field of system safety across all industry sectors, so the articles in this volume offer a wide and historical coverage of safety topics, and give a unique insight into safety engineering over the last 25 years. The topics covered in this volume include: Risk Assessment, Human Factors, Safety Arguments, STAMP/STPA, ISO 26262, the Y2K Problem, Medical Systems, ALARP, Hazards, Software Testing, IEC 61508, Formal...