In this Project on Managing the Atom Discussion Paper, Philipp C. Bleek chronicles nuclear weapons proliferation choices throughout the nuclear age. Since the late 1930s and early 1940s, some thirty-one countries are known to have at least explored the possibility of establishing a nuclear weapons program. Seventeen of those countries launched weapons programs, and ten acquired deliverable nuclear weapons.

Nuclear proliferation to terrorists willing to sacrifice their lives to kill hundreds of thousands of innocent civilians represents a grave threat to the United States and its allies; nuclear proliferation to hostile states poses serious dangers. Yet poorly secured civil research sites with hundreds of nuclear bombs' worth of highly enriched uranium (HEU) and plutonium are scattered around the globe. Because obtaining such material is the greatest hurdle to constructing a nuclear weapon, these sites represent an urgent proliferation threat.