Why do nations obey international law? This remains one of the most perplexing questions in international relations. Nearly three decades ago, Louis Henkin asserted that “almost all nations observe almost all principles of international law and almost all of their obligations almost all of the time.” Although empirical work since then has largely confirmed this hedged but optimistic description, scholars have generally avoided the causal question: If transnational actors generally obey international law, why do they obey it, and why do they sometimes disobey it? The question is fundamental from both a theoretical and practical perspective. It challenges scholars of international law and international relations alike. It vexes all subfields in international affairs, from international security to political economy; from international business transactions to international trade; from European Union law to international organizations. It poses a critical ongoing challenge for U.S. foreign policy, for if we cannot predict when nation-states will carry out their international legal obligations respecting trade retaliation, environmental protection, human rights, global security, and supranational organizations, how can we count on “multilateralism” to replace bipolar politics as the engine of the post-Cold War order? Not least, it remains the daily practical question facing nongovernmental organizations that challenge governmental officials on behalf of victims of human rights abuse. International law and relations scholars have inquired into the power of rules in international affairs for centuries, but the Cold War’s demise, and its implications for the possibilities of international law, have dramatically sharpened interest in the “compliance question.” Within the last decade, the growing perception that “international law does matter” has brought the question to the attention of political scientists, regime theorists, international law practitioners, and legal philosophers. Two recent books, which cap the careers of three eminent international lawyers, represent the most comprehensive and sophisticated efforts to date to address this demanding question. In The New Sovereignty, Harvard Law Professor Abram Chayes, former Legal Adviser to the U.S. State Department, and Antonia Handler Chayes, former Undersecretary of the U.S. Air Force, argue that compliance with international law is best fostered, at least within treaty regimes, by a “managerial model.” In the Chayeses’ view, nations obey international rules not because they are threatened with sanctions, but because they are persuaded to comply by the dynamic created by the treaty regimes to which they belong. “The fundamental instrument for maintaining compliance with treaties at an acceptable level,” they argue, “is an iterative process of discourse among the parties, the treaty organization, and the wider public.” In Fairness in International Law and Institutions, New York University Law Professor Thomas Franck argues that the key to compliance is not so much the managerial process as the fairness of international rules themselves. Threaded with philosophical arguments from his earlier work, and based on his 1993 Hague Lectures in Public International Law, Franck's tour d'horizon of international law asserts that nationsWhy do nations obey international law? This remains one of the most perplexing questions in international relations. Nearly three decades ago, Louis Henkin asserted that “almost all nations observe almost all principles of international law and almost all of their obligations almost all of the time.” Although empirical work since then has largely confirmed this hedged but optimistic description, scholars have generally avoided the causal question: If transnational actors generally obey international law, why do they obey it, and why do they sometimes disobey it? The question is fundamental from both a theoretical and practical perspective. It challenges scholars of international law and international relations alike. It vexes all subfields in international affairs, from international security to political economy; from international business transactions to international trade; from European Union law to international organizations. It poses a critical ongoing challenge for U.S. foreign policy, for if we cannot predict when nation-states will carry out their international legal obligations respecting trade retaliation, environmental protection, human rights, global security, and supranational organizations, how can we count on “multilateralism” to replace bipolar politics as the engine of the post-Cold War order? Not least, it remains the daily practical question facing nongovernmental organizations that challenge governmental officials on behalf of victims of human rights abuse. International law and relations scholars have inquired into the power of rules in international affairs for centuries, but the Cold War’s demise, and its implications for the possibilities of international law, have dramatically sharpened interest in the “compliance question.” Within the last decade, the growing perception that “international law does matter” has brought the question to the attention of political scientists, regime theorists, international law practitioners, and legal philosophers. Two recent books, which cap the careers of three eminent international lawyers, represent the most comprehensive and sophisticated efforts to date to address this demanding question. In The New Sovereignty, Harvard Law Professor Abram Chayes, former Legal Adviser to the U.S. State Department, and Antonia Handler Chayes, former Undersecretary of the U.S. Air Force, argue that compliance with international law is best fostered, at least within treaty regimes, by a “managerial model.” In the Chayeses’ view, nations obey international rules not because they are threatened with sanctions, but because they are persuaded to comply by the dynamic created by the treaty regimes to which they belong. “The fundamental instrument for maintaining compliance with treaties at an acceptable level,” they argue, “is an iterative process of discourse among the parties, the treaty organization, and the wider public.” In Fairness in International Law and Institutions, New York University Law Professor Thomas Franck argues that the key to compliance is not so much the managerial process as the fairness of international rules themselves. Threaded with philosophical arguments from his earlier work, and based on his 1993 Hague Lectures in Public International Law, Franck's tour d'horizon of international law asserts that nations