This book describes a number of the more important improvements in risk assessment methodology in the nuclear industry, developed over the last decade. It presents them in an instructive way so as to be suitable for those wishing to understand the techniques. The methodology of modern probabilistic risk assessment (PRA) is discussed in detail. This book is divided into six parts. Part I, Protecting the Public Health and Safety provides an overview of risk analysis including results presentation, safety goals, emergency planning, and public perception. Part II, the Mathematics, which is necessary to understand the text. Part III, safety Aspects of Light Water Reactors describes the types of plants and goes on to discuss accident initiator selection and frequencies. Part IV, PRA, describes system modelling, human factors analysis, data bases, codes, system interactions, external events, core melt physics, and the transport of radionuclides to the public. Part V discusses 34 types of applications of PRA. Part VI, Resources, provides a glossary, references, and an index. Problems are provided at the end of each part to both stimulate understanding and introduce additional material. This book would be a very valuable addition to the reference library of practitioners in the risk assessment business. It is also a useful instructional text for graduate and undergraduate nuclear engineering students as well as newcomers to the field.