It is noteworthy that East Asian countries' interest in the institutionalization of regionalism has grown under the changing regional landscape, such as the relative decline yet continued presence of the United States and the rise of China. What is the driving force behind these new dynamics of institutionalizing East Asia? This paper examines how the logic of institutional balancing explains East Asian countries' heightened interest in regional institutionalization. The author believes that such a steady progress of institutionalization has been made possible because major countries in East Asia have become both interested in institutionalizing the region and tolerant of other countries' preferences for regional institutions.