This chapter examines postcolonialism, a recent and increasingly influential set of positions and perspectives within the wider discipline of International Relations, and its implications for Security Studies. It first considers the genealogies of postcolonialism, tracing its emergence in a set of transnational debates about the mutually constitutive relations between knowledge and imperialism. It then discusses the standard account of world history as organized around Westphalian sovereignty which informs Security Studies and shows how postcolonialism puts it in question. It also explores the relationship between culture and imperialism according to postcolonialism; Subaltern Studies and its significance to postcolonialism; the concepts of Orientalism and Occidentalism; and how contrapuntal analysis enables a postcolonial critique of Security Studies. The chapter concludes by asking what it might mean to decolonize Security Studies and whether there can be a postcolonial Security Studies.