This essay traces the evolution of the literature on the rationale behind states' pursuit of nuclear weapons, from classical neorealist explanations focusing on relative power to neoliberal institutionalist ones underlining the deterrent power of institutions and constructivist work on the impact of norms, status, and identities. We call attention to their contributions as well as their conceptual and empirical deficiencies and introduce an approach that links both nuclear ambition and nuclear restraint to models of domestic political survival. The inclusion of this previously overlooked independent variable harnesses the utility of extant approaches, allowing more effective weighing of the impact of other causal variables, while accounting for variation over time, across and within states. We take stock of more recent work employing quantitative and qualitative approaches and identify an agenda for advancing causal theories explaining why some states pursue nuclear weapons whereas others do not.