Interest in regional security arrangements is burgeoning in the Asia-Pacific. Discussions about cooperative security either as an alternative or supplement to national defense reflect the concern that some form of cooperative security would provide greater stability than a reliance upon transitory balances of power; and reflect the belief that there should be a less costly and more stabilizing option superior to an exclusive dependence on individual national military buildups that could degenerate into a regional arms race. For Southeast Asia, the institutional solution to the security dilemma is located in ASEAN. In this article, I assess the barriers to a fuller security community in Southeast Asia; the current military situation in Southeast Asia, paying particular attention to the concurrent weapons modernization programs in most of the ASEAN countries; and focus on the role of China as a destabilizing power in the ASEAN region. More generally, I argue that ASEAN is a security community, that there is a set of ASEAN norms which promise greater security cooperation, and that there are real limits to security multilateralism in Southeast Asia.