This dissertation explores how different understandings of power in IR theory lead to different understandings of world order. In particular, I examine how notions of power have informed recent 'debate about empire' and what the term empire might usefully mean in the context of contemporary international relations. I start by investigating how power is understood in relation to the role of shared understandings. Mainstream or "Rationalist" scholars of IR have argued that shared norms and principles are epiphenomenal, existing only to the extent that sovereign states find utility in them. 'Reflectivist' scholars, on the other hand, have suggested that we attribute a much greater degree of autonomy to what they call "constitutive knowledge". That is, the intersubjective and historically contingent truths about world politics that inform the values and norms of state behavior. What is noteworthy about the recent debates about "empire" is that, for better or for worse, Rationalist scholars have tended to explain America's recent unilateralism in terms of a return to the logic of political realism which gives primacy to state power. However, following the Reflectivist argument, I argue that it is a mistake to limit the analytic scope of unilateralism to the egoistic agency of any one state. Instead, it may be more precise to situate American unilateralism in the context of an emerging regime or formation of shared understandings which is more global in scope. To explore this possibility, I turn to Foucault's theory of power which explores how liberal governments both direct their populations and rationalize the use of certain forms of violence. I turn also to Hardt and Negri who, taking their lead from Foucault, offer a novel definition of the term empire as a quality or condition of the practice of global governance particular to late modernity. Hardt and Negri define empire as a new form of global sovereignty that has emerged along with the global market and global circuits of production. My research explores how this definition can be used to refine such key concepts and categories of IR theory research as sovereignty, political economy and security. Through the reinterpretation of these key categories, I show how theories based on constitutive knowledge are capable of recognizing that there is in fact a great deal more going on in contemporary global power relations than American unilateralism.