Information-sharing and maritime domain awareness (MDA) are at the heart of the contemporary maritime security agenda. The goal of MDA is to develop a shared understanding of developments and threats at sea which is one of the preconditions for coordination and cooperation between diverse maritime security agencies. MDA is not only a technical challenge, but also a social, political, and legal one. A study of the organization of MDA in the Southeast Asian region with a focus on its three major centers is presented, and the political and social functions that each center performs in the governance of maritime security in the region are explored. The lessons that the Southeast Asian system offers for the organization of MDA in other regions are also outlined with particular reference to the Western Indian Ocean.