Why is it that the World Bank has failed to effectively incorporate the impact of regionalisation within its economic development strategies and policy advice for borrowing countries? This is an interesting puzzle given the increasing importance that scholarly observers, policy practitioners and development agencies have attached to regionalism and regionalisation in recent years. In the fiscal years 1995?2005, the World Bank provided only US$1.7 billion in support for regional (or multi-country) operations across the globe?this is less than 1 percent of its project and other funding overall. In South-East Asia, while the Asian Development Bank has had a particularly strong engagement with regionalism, the World Bank has only recently started to come on board with regional analysis and programs. The article proposes that the gap is due to a combination of institutional and ideological factors, and explores this proposition through a study of the World Bank in Vietnam.