There is a growing understanding among maritime security practitioners of the importance of Maritime Domain Awareness (MDA) as an essential enabler of maritime security. This article describes Australia's efforts to develop an integrated national MDA system that brings together data and intelligence from a range of military and civil agencies and commercial sources to which a risk-based assessment is applied. This has become an essential tool to combat transnational maritime security threats in the Indian Ocean and elsewhere. But inherent limitations of national MDA systems are also pushing Australia and other countries to cooperate in trying to improve MDA. This paper then examines ways in which Australia can promote MDA cooperation in the Indian Ocean. It considers the effectiveness and limitations of current and proposed multilateral information sharing arrangements in the region. It concludes that Australia should primarily focus on working with selected Indian Ocean partners to enhance information sharing and help develop integrated national MDA systems.