The end of the Cold War is only one in a series of events that have radically modified the operational environment of international organizations since their establishment. These changes, many of which have lately been discussed under the term ""globalization,"" include: decolonization; growing awareness of the global nature of many economic, environmental, and public health problems; multiplication of non-governmental organizations; globalization of mass media and the market; rapid developments in the field of biotechnology; and the emergence of new information technologies, particularly the Internet. These developments suggest that the time has come to take a fresh look at the philosophy of international organization. The Legitimacy of International Organizations presents the results of an interdisciplinary research project of the Peace and Governance Programme of the United Nations University. The authors are prominent experts in the fields of social and political philosophy, law, political science, economics, and environmental studies.