This fourth edition provides wide-ranging coverage of the structure, internal workings, policies and performance of international organizations such as the UN, EU, IMF and World Bank. The authors take a unique approach to international organizations, arguing that they are best understood as political systems that convert problem ‘inputs’ into policy ‘outputs’, effecting varying levels of change. Using this framework, International Organization unpacks the constitutional and institutional complexities of IOs, covering contemporary political concerns like nuclear disarmament, climate change and human rights protection, as well as trade, monetary and financial relations, and international development. The edition has been updated throughout to explore key policy areas such as the war in Ukraine, collective defence and NATO, as well as the increasingly urgent issue of migration and refugee policies. The authors also attend to the issue of biodiversity. New to this edition: · Coverage of new academic debates and contemporary developments in the field · A new chapter on regional cooperation, which contrasts the European Union with the African Union, MERCOSUR and ASEAN · A new conclusion on the ‘crisis of international organizations’ attending to debates on the legitimacy of IOs, the rise of emerging powers, the difficulty of extending global governance to new areas such as cyber and AI, and the increasing geopolitical use of IOs This is a key text for undergraduate and postgraduate students of politics and international relations; it is essential reading for those taking courses on international organization, global governance, the UN, and globalization.