The year 1997 marks a significant change in East Asian regionalism. Since the economic crisis of 1997, both Southeast and Northeast Asian countries have worked hard to reshape the regional political configuration in the process of encountering the economic crisis in East Asia. Southeast Asian countries, in particular, played a pivotal role, as the main vehicle, in initiating the widening of East Asian regional cooperation. The very first move of Southeast Asian countries to encounter the ever-present economic turmoil was to invite three major Northeast Asian countries, South Korea, China and Japan, into the annual ASEAN submit at the end of 1997. Since that, the ASEAN+3 regional cooperation mechanisms have been rapidly institutionalized within a relatively short period. Along with the regularly-held annual ASEAN+3 submit, various levels of governmental meeting were held more than 40 times per annum. Considering the weak traditions of regional cooperation in this region, what happened during the last decade since the economic crisis of 1997 was the remarkable achievement. What is more important is that ASEAN, though its weak diplomatic position, has played a substantial role as a driving force in the whole process of East Asian regional cooperation. This study analyses the motives, backgrounds and details of how ASEAN as a single unit has been able to initiate and develope the regional cooperation mechanism in East Asia since the economic crisis.