Although international relations theory has been dominated for two decades by debates over theories of international politics, recently there has been a surge of interest in theories of foreign policy. These seek to explain, not the pattern of outcomes of state interactions, but rather the behavior of individual states. The author surveys three prominent theories of foreign policy and shows how the works under review set out a compelling alternative, one that updates and systematizes insights drawn from classical realist thought. Neoclassical realism argues that the scope and ambition of a country's foreign policy is driven first and foremost by the country's relative material power. Yet it contends that the impact of power capabilities on foreign policy is indirect and complex, because systemic pressures must be translated through intervening unit-level variables such as decision-makers' perceptions and state structure. Understanding the links between power and policy thus requires close examination of both the international and the domestic contexts within which foreign policy is formulated and implemented.