A growing literature posits the importance of boundaries in structuring social systems. Yet sociologists have not adequately theorized one of the most fraught and consequential sites of boundary-making in contemporary life: the delineation of the official edges of the government—and, consequently, of state from society. This article addresses that gap by theorizing the mechanisms of state boundary formation. In so doing, we extend culturalist theories of the state by providing a more specific model of how the state-society boundary is produced. Further, we contribute to institutionalist accounts of politics by highlighting boundary-work during policy creation as a crucial site of political struggle, one with causal implications insofar as it illuminates a process that determines fine-grained distinctions in policy forms.