It is now a little over ten years since a group of us representing government departments and the professional institutions gathered at the headquarters of the UK Health and Safety Executive. We were trying to decide what action we might take given a growing concern in the trade press and among professionals about the way in which we were managing the development of safety-critical computer-based systems.

At that time there was much misunderstanding. We all came from different industry sectors, with different traditions, different regulatory requirements, different standards, and different ways of managing computing technology in critical applications.

It is clear from the sheer diversity of work reported in this book that there are still many differences. Moreover, technology and the market have both developed dramatically during those ten years, complicating the picture still further. But over that time we have built a community with at least a better mutual understanding.

In particular we have recognised that there are no simple solutions: but we have generally agreed strategies such as those embodied in the IEC 1508 Standard, in the general principle of the safety case, and in the evolving form of a safety case. These give us a framework for incorporation of more knowledge as we acquire it. There is certainly much more to be learned.

The next challenge is to find ways to encapsulate some of our understanding for others who are not part of this research community but are simply building systems - increasingly, safety critical systems. Telling them the big lesson that we have learned - that the problem is more difficult than we had appreciated - does not help them a lot.

There are many to thank for their support and patience during the work reported here, apart from the researchers themselves. There are the professional institutions, the individuals who gave their time and their employers, and, of course, the DTI and the EPSRC who, with industry, funded the programme which supported much of the work.

I would finally like to thank Mike Falla for his diligence in making such a coherent presentation of the work reported here. As co-ordinator for the programme, I have often said that my ambition was to engender greater mutual understanding through comparison and contrast of a broad range of technologies, applications, and industrial environments. I claim to have done the easy bit - to create the contrasts. Mike has done the more difficult bit - the considered comparison of these ideas and activities.