This book looks at the problems of determination of safety and the underlying concept of safety itself. It is believed that if certain pervasive themes are properly appreciated, the whole field of safety will be better understood. The first chapter of the book sketches the general nature of safety decisions, defining safety as a measure of the acceptability of risk. Chapter two presents the diverse problems of measuring risk. Chapter three describes how the acceptability of risks is appraised. Chapter four discusses personal roles, the functions of institutions the development and resolution of controversies, and the issue of responsibility. Chapter five describes how knowledge and judgment are applied in devising safeguards. In chapter six DDT is used as an example in which these issues can be reviewed. Finally, there is an afterword and a list of sources of documents. (BB)