Trust and Mistrust in International Relations. By Andrew H. Kydd. Princeton: Princeton University Press, 2005. 284p. $39.50.

That cooperation is at best difficult and at worst impossible in the anarchic international system is an established idea. Analyses usually assume that state preferences put them in a prisoner's dilemma where defection is the strictly dominant strategy. Explaining cooperation means showing why actors forgo the short-term benefits of exploiting others. Mechanisms involve conditional play, institutional arrangements, and hegemonic leadership, which help overcome coordination, monitoring, enforcement, and free-rider problems.