This chapter recapitulates the book’s core themes and arguments, opening with George Curzon 1907 lecture on ‘Frontiers’. Drawing on the famous American ‘frontier thesis’ of Frederick Jackson Turner, Curzon positioned imperial frontiers as spaces of excess and threat that held out the promise of national and racial salvation for Britain. By the age of high empire, agents of empire in India widely conceived of frontiers as spaces of productive tension between closure—in the form of clearly delineated borders, normalised and bureaucratised administration, and authoritative knowledge of people and space—and openness—in the form of spatial, epistemic, and administrative indeterminacy. They laboured to render the outskirts of empire ‘other spaces’, requiring distinctive types of knowledge and government under the unfettered guidance of ‘men on the spot’.