In Vietnam, regionalisation in the GMS occurs in different parts at different paces and levels driven by thecentral government and with the participation of the local governments, private sector and grassrootspeople in the framework of the GMS Program. So far there has been no major research either in Vietnameseor English that addresses this issue. The thesis seeks to fill this gap by examining the empirical process ofregionalisation in three Vietnam’s border towns in the First-Generation GMS Economic Corridor TownDevelopment Project. Employing analytical framework based on relevant International Relations andinterdisciplinary theories, and a mix of qualitative and quantitative methods, the thesis finds that the GMSregionalisation is a combination of ‘top-down’ and ‘bottom-up’ processes. The thesis commences byhighlighting the significance of the Mekong River to the development of the region. Then various multilateralcooperative schemes are explored to generate a complete picture of regional cooperation. It is concludedthat many multilateral mechanisms with little progress may have negative impacts on the regionalisation inthe GMS. Among 13 schemes in the GMS, GMS Program is considered as one of the most well-knownsubregional cooperation schemes. The GMS Program came to existence just in time to assist the Mekongriparian states to integrate better into the regional and international markets in the context that there werenew developments both at the regional and world’s levels. In the case of Vietnam, the GMS Program hasgiven Hanoi an option to carry on its omni-directional foreign policy and helped it consolidate its existingrelationships with its traditional and neighbouring partners. Notably, regionalisation is occurring in someparts of the country where GMS projects have been implemented. Regionalisation can be best observed ineconomic space where there are intensive interactions among people under various dimensions enabledby favourable policies. Although regionalisation promises to bring new cooperative opportunities in theGMS, regionalisation in the GMS will continue to meet new challenges from growing natural and man-madethreats to the Mekong River. Further, the involvement of outsiders is also a real challenge to the regionbuildingprocess.