A groundbreaking examination of a central question in international relations: Do states act rationally? To understand world politics, you need to understand how states think. Are states rational? Much of international relations theory assumes that they are. But many scholars believe that political leaders rarely act rationally. The issue is crucial for both the study and practice of international politics, for only if states are rational can scholars and policymakers understand and predict their behavior. John J. Mearsheimer and Sebastian Rosato argue that rational decisions in international politics rest on credible theories about how the world works and emerge from deliberative decision-making processes. Using these criteria, they conclude that most states are rational most of the time, even if they are not always successful. Mearsheimer and Rosato make the case for their position, examining whether past and present world leaders, including George W. Bush and Vladimir Putin, have acted rationally in the context of momentous historical events, including both world wars, the Cold War, and the post–Cold War era. By examining this fundamental concept in a novel and comprehensive manner, Mearsheimer and Rosato show how leaders think, and how to make policy for dealing with other states.