This book provides a comprehensive overview of the evolution and particularities of regional organizations across Africa, the Americas, Asia and Europe since 1945. The authors analyze the membership dynamics and policy scopes of 76 organizations, and compare their opportunities and challenges in regional governance. They consider organizations' competencies in eleven different policy areas, including trade, security and environment, and trace patterns in their development. For those with interests in comparative regionalism, international relations, political science and international law, this is an essential companion to some of the world's most significant organizations.