International relations are full of appeals to and claims aboutinternational law. From intellectual property, to human rights, to environment,to investment, to health and safety, issues that have traditionally been almostexclusively within the purview of domestic lawmakers are now the subject ofinternational legal obligations. Yet despite the importance of internationallaw, there are no well-developed set of theories on the ways in whichinternational law impacts domestic decision makers. Filling a conspicuous gap in the legal literature, Andrew T. Guzman's HowInternational Law Works develops a coherent theory of international law andapplies that theory to the primary sources of law, treaties, customaryinternational law, and soft law. Starting where most non-specialists start,Guzman looks at how a legal system without enforcement tools can succeed. Ifinternational law is not enforced through coercive tools, how is it enforced atall? And why would states comply with it? Supporting the traditional international law view that international lawmatters and affects state behavior, Guzman offers a theory of international lawthat assumes states behave rationally and selfishly. The author argues that atthe heart of compliance with international law is the basic fact that a failureto live up to legal obligations today will impact a country's ability to extractconcessions for legal promises in the future. Under this reputational model, theviolation of international law generates a costly loss of reputation and thethreat of this loss provides an incentive to comply. A reputational theorysuggests when and where international law is likely to be effective and ways tomaximize its ability to advance the goal of international cooperation.Understanding international law in a world of rational states helps us tounderstand when we can look to international law to resolve problems, and whenwe must accept that we live in an anarchic world and must leave some issues topolitics.

Andrew T. Guzman is Professor of Law and Director of the International Legal Studies Program at Boalt Hall School of Law, at the University of California, Berkeley. He has written extensively on international trade, international regulatory matters, foreign direct investment and public international law and has published in law, economics, and political science journals.