Comprising contributions from scholars, analysts and policymakers, this volume explores and debates how and why regional bodies such as the European Union (EU) and the Association of Southeast Asian Nations (ASEAN) are formed and sustained. Furthermore, it examines the drivers of, and impediments to, regionalism and integration. The debates regarding what and who constitute drivers are presented in a fresh, thematic and comprehensive manner. Leadership and core states are also critically examined, whilst material, ideational and normative factors are all assessed comparatively. Significantly, in light of the global financial crisis, the book considers the role of crisis as a driver of regionalism and integration.