This chapter provides a theoretical framework for the book. It briefly notes the evolution of debates about security in international relations thought before making a case that security can be understood as a social construction, given meaning by particular political communities in different ways at different times. These different meanings can be classified in terms of discourses – specific accounts of threat, referent object, agents of security and means of achieving it. After differentiating this account from the prominent Copenhagen School conceptual framework of securitization, the chapter notes the importance of conceiving security as a site of contestation and negotiation. It points to the political significance of the promise of providing security – the politics of security – and the ethical assumptions and implications of alternative accounts of security – the ethics of security.