Realism is the oldest and most venerable school of thought in the study of international politics. Thucydides, Hobbes, and Machiavelli provided its classic texts, and Hans Morgenthau, George Kennan, Henry Kissinger, Kenneth Waltz, and others brought it into the twentieth century. In recent decades, however, realism has been transformed into a rational-choice theory, in which states are thought to be pursuing security strategies under conditions of anarchy, and Williams, dissatisfied with this rationalist turn, joins a growing group of young scholars who are returning to classical realist writings in search of more complex and historically contingent insights. He focuses on three great realist thinkers (Hobbes, Rousseau, and Morgenthau) and finds in each not simply a discussion of anarchy and realpolitik, but also more involved arguments about ideas, social knowledge, and the limits of reason. In Williams' rendering of classical realism, the international political order is a constructed realm where power and insecurity mix with the search for consent, legitimacy, and the restrained exercise of power. This is not a vision of realism that most realists will recognize, nor one that yields clear empirical propositions; in the end, Williams leaves us with a realism so nuanced and shaded that it provides few useful tools with which to explain real-world politics.