Nuclear weapons are widely regarded as one of the most lethal aspects of military arsenals ever created. As such, international relations and security experts have long been concerned about their proliferation. To prevent the spread of nuclear weapons, both policymakers and academic researchers have focused on what are commonly thought to be the primary drivers of proliferation: security concerns and domestic politics and economies. This brief examines another important driver: the role of national leaders themselves. Based on a study of 1,400 leaders in office between 1945 and 2000, author Ellen Park shows that leader personality and experience drive decisions about whether—or not—to pursue nuclear weapons, a finding that holds true across countries (rather than being limited to a few unique cases). Put simply, the pursuit of nuclear weapons is systematically influenced by certain attributes of leaders, such as college major, socioeconomic background, and military and international experience. To predict when and where the spread of nuclear and other emerging technologies will emerge next, policymakers should promote interdisciplinary dialogue to cultivate leader profiles and expand their use.