This is a state-of-the-art report prepared within the UNU/WIDER project The New Regionalism and the International System - Implications for Development and Security, covering East and Southeast Asia. The report constitutes an initial inventory study on regionalization incentives and prospects and is arranged around the three themes of economic development, regional security and ecological problems. It is basically a study of secondary material with an extensive bibliography.The aim of the report is, first, to provide a survey of recent literature regarding regionalization and regional cooperation in East Asia in general and in Southeast Asia in particular, and, second, to review a number of historical and contemporary debates in regard to the potential regionalization process in East Asia-Pacific in general and in Southeast Asia in particular. To satisfy these vast aims, the report therefore tries to give the reader advice on where to find further readings.The UNU/WIDER project mentioned above acknowledges a number of new features of regional cooperation in the world and the theoretical point of departure for this report - as well as for the larger research programme of which it is a part - is the new regionalism which, it is argues, goes beyond the more traditional debates on regional cooperation. It attempts to display signs of multidimensionality and 'from within approaches. These tendencies are explored and described through discussions on concepts such as open regionalism and new regionalism.The report takes note of recent literature on world regionalization before it lists the most important regional initiatives in East and Southeast Asia. It observes the current imbalance between drastically increased regional economic interactivity coupled with the absence of, or very low keyed, political mechanisms for handling this situation. It argues that there is a need for enhanced political/security cooperation in order to sustain the current transformation process in East and Southeast Asia. Increased regional cooperation on a wide range might be the answer to this question. The report elaborates here on what a maximalist and minimalist approach to regionalization would mean. A version of the maximalist approach could be a developed APEC, while the minimalist version is an extended ASEAN; it is likely that somewhere in between these poles, we will find a future, deepened, regional cooperation.The report reviews various East and Southeast Asian debates pertinent to the question of regionalization. The underlying factors for further regionalization are mentioned briefly for East Asia and, in somewhat more detail, for Southeast Asia before a number of scenarios are discussed and a tentative conclusion is drawn.The report concludes that there are hectic activities in terms of regionalization in East and Southeast Asia. There are, however, severe obstacles to institutionalized regionalization. This does not necessarily stop the process, but rather makes it uncertain in terms of its scope, depth and future direction. The conclusion also gives prominence to a number of key questions such as: the pivotal relation between the US and Japan, the relation between Japan and Southeast Asia, the extension of ASEAN to Indochina and the nature and degree of Asian exclusiveness in any East Asian regional cooperation formula.