Regionalism and regional integration in East Asia has developed dynamically at various levels over the past two decades. In the world system, East Asia's degree of regional economic coherence is second only to the European Union's. In addition to deepening micro-level regionalisation, new regional frameworks and organisations have emerged, centred on an East Asian collective of nations and economies.;This paper examines the development of new regional institutions involving the whole East Asia region, focusing on four 'supra-structure institutions': ASEAN Plus Three, East Asia Summit, Asia-Europe Meeting, and Asia-Pacific Economic Co-operation forum, and two 'supporting institutions': Pacific Basin Economic Council and Pacific Economic Cooperation Council. Particular attention is made to what likely future regional institutional architecture centred on East Asia may emerge over forthcoming years, and the following core arguments are made. Owing to issues of 'variable geography', the constituent membership of an East Asian region is open to contestation and East Asia's patterns of regional economic coherence are to some extent in a constant state of flux. The formation of an East Asian regional community will also depend on an alignment of national interests, development-related imperatives and ideological factors, and primacy will come to the regional institution that develops the most effective instruments of regional co-operation and integration.;The paper argues that this will probably be ASEAN Plus Three, which has the most realistic prospects of advancing regional economic integration. Each regional institution should functionally specialise, the larger grouping of EAS, ASEM and APEC concentrating for example on developing their multilateral utility regarding global governance issues. Finally, fostering a more functionally effective partnership between Japan and People's Republic of China is vital to the future prospects of East Asia's regional community-building.