The Nuclear Non-Proliferation Treaty is considered the model for how to address the complex problem of proliferation. This article analyzes the NPT's impact on the decision to peacefully give up nuclear weapons programs in four states-South Korea, Argentina, Brazil, and Libya. It concludes that while the nuclear decision-making calculus is complicated, because of the centrality of security concerns in nuclear decision-making, the NPT as currently structured appears not to have had a meaningful impact. This article accordingly suggests that nonproliferation efforts should focus on working directly with problem states to alter their calculations about the utility of nuclear weapons.