Political theology is a broad and diverse series of investigations into the structural relationship between theology and politics – particularly the way that theological categories come to underpin modern political concepts, practices and institutions, such as sovereignty, the nation state and democracy. In this chapter I suggest that political theology is fundamentally concerned with the problem of legitimacy and that it refers to the absent place of the sacred in modern secular societies. As a mode of enquiry, it provides us with an alternative framework in which to understand modes of political experience that cannot be adequately grasped by conventional political theory. The chapter explores the origins of the concept, then turns to Carl Schmitt's influential interpretation of political theology as a secular translation of theological concepts into modern ideas of the sovereign state. It is argued that Schmitt's political theology is a justification for an authoritarian notion of sovereignty defined through the unilateral state of exception. The chapter then turns to alternative post-Schmittian approaches, including more radical interpretations of political or public theology that can inform social and racial justice struggles and climate action. Recent interventions in eco-political theology and economic theology are also considered.