Since September 11, 2001, most expert commentary on radiological weapons has focused on nonstate actors, to the neglect of state-level programs. In fact, numerous countries in the past have expressed interest in radiological weapons; a number have actively pursued them; and three tested them on multiple occasions before ultimately deciding not to deploy the weapons. Why is so little known about these false starts, especially outside the United States? Are such weapons more difficult to manufacture than depicted by science-fiction authors and military pundits? Are radiological weapons a thing of the past, or do they remain an attractive option for some countries? A comparative analysis of the previously underexplored cases of radiological weapons programs in the United States and the Soviet Union illuminates the drivers and limitations of weapons innovation in one specific nuclear sector. An examination of the rise and demise of radiological weapons programs in both countries also points to circumstances in the future that might prompt renewed interest on the part of some states in radiological weapons and proposes steps that might be undertaken to reduce the possibility of their production, deployment, and use.

Although projections of nuclear proliferation abound, they rarely are founded on empirical research or guided by theory. Even fewer studies are informed by a comparative perspective. The two books under review— The Psychology of Nuclear Proliferation: Identity, Emotions, and Foreign Policy , by Jacques Hymans, and Nuclear Logics: Alternative Paths in East Asia and the Middle East , by Etel Solingen, are welcome exceptions to this general state of affairs, and represent the cutting edge of nonproliferation research. Both works challenge conventional conceptions of the sources of nuclear weapons decisions and offer new insights into why past predictions of rapid proliferation failed to materialize and why current prognoses about rampant proliferation are similarly flawed. While sharing a number of common features, including a focus on subsystemic determinants of national behavior, the books differ in their methodology, level of analysis, receptivity to multicausal explanations, and assumptions about decisionmaker rationality and the revolutionary nature of the decision. Where one author emphasizes the importance of the individual leader's national identity conception in determining a state's nuclear path, the other explains nuclear decisions primarily with regard to the political-economic orientation of the ruling coalition. Notwithstanding a tendency to overinterpret evidence, the books represent the best of contemporary social science research and provide compelling interpretations of nuclear proliferation dynamics of great relevance to scholars and policymakers alike.