Thomas Pangle and Peter Ahrensdorf provide a critical introduction to the most important conceptions of international justice, spanning 2,500 years of intellectual history from Thucydides and Plato to Morgenthau and Waltz. Their study shows how older traditions of political philosophy remain relevant to current debates in international relations, and how political thinkers through the centuries can help us deepen our understanding of today's stalemate between realism and idealism.