Assuring the Safety of Systems contains papers presented at the twenty-first annual Safety-Critical Systems Symposium, held in Bristol, UK, in February 2013. The Symposium is for engineers, managers and academics in the field of system safety, across all industry sectors, so the papers making up this volume offer a wide-ranging coverage of current safety topics, and a blend of academic research and industrial experience. They include both recent developments in the field and discussion of open issues that will shape future progress. The topics covered by the 20 papers in this volume include safety certification, regulation and acceptance in a number of industry sectors; identification of potentially hazardous control actions; safety cases; product safety; risk management; formal methods; hazard analysis; formal proofs and testing; the balance between designed-in and procedural approaches to safety; human factors; and safety culture. This book will be of interest to both academics and practitioners working in the safety-critical systems arena.