What is the relationship between nuclear postures and nonproliferation policies, and the spread of nuclear weapons? At first blush, this might appear to be an obvious question. After all, states go to great lengths to prevent the spread of nuclear weapons—extending nuclear security guarantees to nonnuclear weapon states; forward-deploying nuclear weapons on the territory of allies; sizing their own nuclear arsenals with the proliferation decisions of other states in mind; supporting international institutions in conducting inspections of nuclear facilities in nonnuclear weapon states; restricting the availability of sensitive nuclear technology; applying and enforcing sanctions against would-be proliferators; conducting military strikes against nuclear facilities; and promoting nuclear cooperation for peaceful purposes—among many other steps. It would be strange to imagine that states pursue such actions unless they can expect a policy payoff in terms of peace or security. Yet, there is little systematic evidence to suggest that nuclear postures and policies have a meaningful impact on the spread of nuclear weapons.