The article sets out to gauge the usefulness of the concepts of legitimacy, sovereignty and nation in theorising a specific, South-East Asian case of nation building. It looks at the interplay between nation building and regionalist ideology in Vietnam, within the context of the Association of South-East Asian Nations (ASEAN). As one of the world's last communist states, the way in which Vietnam has reconciled hard-won sovereignty with regionalisation is all the more intriguing. The article distinguishes the state-led ideology of regionalism from the macro-level process of regionalisation in charting how sovereignty, legitimacy and nation are constructed in the Vietnamese case, with a view to drawing parallels with experiences in other regions. The first section looks at the concepts of legitimacy, sovereignty and nation and how they underpin the state construct, before relating these to Vietnam's ongoing nation-building project in the second section. The final section evaluates the evolution of these concepts within a regional framework, with specific reference to Vietnam's experience as a member of ASEAN. It concludes that official nation building in Vietnam continues to be based on the premises of state sovereignty and legitimacy, an approach eminently compatible with 'the ASEAN way'. The Vietnamese Communist party seeks to reconcile regionalism with its ongoing nation-building project in a bid to bolster both domestic legitimacy and external sovereignty.