Presenting the principles of human health risk analysis as they are applied in environmental decisions, this study balances the discussion of scientific theory and methods, philosophical analysis, and applications in regulatory decisions. The material is directed towards risk analysts who must apply their skills in a policy setting, and towards policy analysts who must use risk estimates. The presentation is suited ideally as an introductory text on the methods of risk analysis and on the cultural issues that underlie these methodologies. The work is designed around a series of detailed case studies of environmental risk analysis which walk the reader from the historical nature of the problem, to the formulation as a risk-based problem, to the conduct of risk analysis, and on to the application, debate, and defence of the risk analysis.