On May 29 and 30, 1985, a workshop was held to explore the legal, ethical, social, scientific, and practical aspects of the use of the de minimis risk concept for health and safety regulation. The workshop was sponsored by the Society for Risk Analysis and its National Capital Area Chapter, the Environmental Protection Agency, the Nuclear Reg- ulatory Commission, and the Electric Power Research Institute. The two-day meeting was held in Washington, D. C., at the Brookings Institution; however, the Brookings Institution was not a sponsor of the meeting and did not playa role in its program. De minimis risk policy considerations were addressed from a theoretical and phil- osophical viewpoint, from a quantitative and methodological basis, and through insights gained with regulatory applications. The distinctions between these three approaches to the subject are not sharp; most papers in these proceedings address aspects of all three topics. The reader familiar with the literature on the use of risk assessment in regulatory policy and decision making will find significant new contributions to the field. One of these is the examination of regulatory actions-in particular actions by the EPA-in response to risks of varying magnitude. Many attempts to seek patterns in regulatory policies have been based on analysis of the implicit economic value in obtaining risk reductions. These analyses have typically found great variability in the marginal cost- 1 effectiveness of regulatory actions.