At present, International Relations scholars use the metaphor of ‘state socialization’ in mutually incompatible ways, embarking from very different starting points and arriving at a bewildering variety of destinations. There is no consensus on what state socialization is, who it affects, or how it operates. This article seeks to chart this relatively unmapped concept by defining state socialization, differentiating it from similar concepts, and exploring what the study of state socialization can contribute to important and longstanding theoretical debates in the field of international relations.