Realism remains the most important and controversial vision of international politics. But what does it mean to be a realist? This collection addresses this key question by returning to the thinking of perhaps the most influential realist of modern times: Hans J. Morgenthau. In analyses of issues ranging from political philosophy, to international law, to the impact of nuclear weapons and the challenges of American foreign policy, the authors demonstrate that Morgenthau's thinking exemplifies a rich realist tradition that is often lacking in contemporary analyses of international relations and foreign policy. At a time when realism is once again at the centre of both scholarly and political debates, this book shows that the legacy of classical realism can enrich our understanding of world politics and contribute to its future direction.