Over the past few decades states all around the globe have intensified institutionalized cooperation at the regional level. To deepen our understanding of state-led regionalism, the authors use an analytical framework comprising four main strands. First, they describe and explain the genesis and growth of regional organizations. Second, they account for institutional design, looking at important similarities and differences. Third, they examine the interaction between organizations and member states in an attempt to reveal factors that shape the level of commitment to and compliance with regional initiatives. Finally, they consider the impact of regional organizations on their member states. They conclude by providing a foundation for future research on the dynamic development of regionalism.