From the dawn of the modern period in the seventeenth century through to contemporary times, the existence of the nation-state has been the central organizing principle of the international system. Arguably, modernity in its most concrete form is inseparable from the modern idea of the nation-state to which it gave birth. However, debate about the moral basis of international relations is as old as the system itself. Today, as in the past, the recurring questions animating the debate about the role of the state in international relations include: Is the international system as the political realists maintain essentially anarchic, marked by competition among independent states pursuing their national interest and power, or does international relations provide a context of norms by which nations may be said to form a society of states? Does justice among nations rest on the core principles of deference towards sovereignty and nonintervention, or is humanitarian intervention and the use of force to punish wrongdoing and protect the innocent justified by an overarching standard of international morality? Given the continuing theoretical and ethical debates in the supposedly “postmodern” twenty-first century about the rights and responsibilities of sovereign states and the limits and possibilities of international law and institutions, there is no less urgency now than perhaps at any other time in the past to inquire: What, if anything, does it mean to speak of morality in international relations?