The debate between realists and liberals has reemerged as an axis of contention in international relations theory. Revolving in the past around competing theories of human nature, the debate is more concerned today with the extent to which state action is influenced by “structure” (anarchy and the distribution of power) versus “process” (interaction and learning) and institutions. Does the absence of centralized political authority force states to play competitive power politics? Can international regimes overcome this logic, and under what conditions? What in anarchy is given and immutable, and what is amenable to change?