Will the Indo-Chinese enlargement of ASEAN undermine regional economic integration, or does it have the potential to help consolidate and advance economic integration in Southeast Asia? This paper argues that the Indo-Chinese enlargement of ASEAN has the potential to enhance ASEAN economic integration by helping to extend the dimensions of the ASEAN regional market and the range of internal industrial conplementarities, this market offers to investors. These potential economic gains will, however, remain unrealised if regional economic integration is undertaken in a manner that ignores socio-economic divisions within and between states. If the benefits of liberalisation and integration are not distributed more equitably amongst populations, then we are likely to see growing challenges to these processes. A 'two tiered ASEAN' divided between a richer core of original members and a set of poorer, under-developed new members, consequently, threatens the future of ASEAN economic integration. However, the notion of a 'two-tired ASEAN' should not blind us to the fact that socio-economic divions also exist in the original members as well, notaby in Indonesia but also in Thailand and the Philippines. Thus, a key challenge for ASEAN economic regionalism in the future, and one that poses a crucial test for Indo-Chinese states, is that of governance for development at both the regional and national levels to ensure that growth, equity and social justice are delivered. The paper concludes with a bried discussion of some key regional-level programmes that are in place to address such concerns.