This dissertation project examines the governing narrative of the Cold War in order to understand how particular values and purposes came to dominate risk analysis. It casts risk analysis's regulatory history in a new light by showing that it was not established in the late 1970's, as most accounts claim, but much earlier. Case studies of civil defense planning, nuclear reactor safety, and the controversy over nuclear fallout show a) that risk analysis emerged early in the Cold War to meet policy objectives similar to those characteristics of later risk analysis, and b) that changes in methodology and regulatory sites marked its reestablishment in the late 1970's. This effort to reinstitute early Cold War patterns of authority and values in the wake of the social upheavals and regulatory reforms of the sixties marked a new and still unresolved phase in a conflict between system learning and social learning. The study argues that current tensions between authoritarian and democratic approaches to regulatory risk are indicative of an underlying choice about alternative forms of modernization.