The principles, values, and manifestations of multilateralism, including the United Nations, are under sustained scrutiny and assault. Their performance and effectiveness are questioned, as are their decisionmaking procedures and their representation, according to 21st-century standards of accountability and democracy. All of this has a corrosive effect on their legitimacy. Multilateralism under Challenge? explores the performance and future of multilateral approaches and institutions with reference to major global problems such as terrorism, weapons of mass destruction, HIV/AIDS, environmental sustainability, economic justice, human rights, and humanitarian assistance. “Multilateralism is an essential component of international life, as the contributions to this volume clearly demonstrate. We need to make multilateralism more effective and more accountable, to be sure. This book advances constructive ideas on how to do just that.” —John G. Ruggie, Harvard University