The safe operation of computer systems, in both their software and hardware continues to be a key issue in many real time applications, when people, environment, investment or goodwill can be at risk. Such applications include the monitoring and control of high energy processes, of nuclear and chemical plants, of factory automation, of transportation systems, or funds transfer and of communication and information systems. This book represents the proceedings of the 1987 Safety and Reliability Society Symposium held in Altrincham, UK, 11-12 November 1987. It is thus part of the series of proceedings for Society Events, which in previous years have not addressed the topic of the Safety and Reliability of Computer Systems. The book is also part of another series of reports, and is closely related to the Elsevier Book "Safety and Reliability of Programmable Electronic Systems" which I edited in 1986, and the series of workshops known as SAFECOMP held in 1979, 1982, 1983, 1985, 1986 which are referenced in some of the papers. The structure of the book represents the structure of the Symposium itself. The session titles, and the papers as selected represent the current practice in many industries. The trend is towards more industrial usage of Formal Methods, and tools to support these methods, whilst continuing to make best use of Software Engineering, Safety and Reliability Assessment, and accumulated experience.