The Mekong Basin is rich in water and other resources, and the six countries that share it include some of the world’s poorest on a per capita income basis. They also include some of the world’s fastest growing economies. Two of the countries also have fast growing rural populations. The Mekong is a shared resource. It is shared across borders, among more than 60 million people who live in the basin, between those who live in the basin and others who draw on its resources, between farmers, fishers, power producers, consumers and many others. Water appropriation for human use is currently only about 12 per cent of total flow. Although dams currently regulate only five per cent of the waters in the basin, many large hydropower dams have been proposed or are under construction. Environmental issues include the need to maintain the seasonal water flows that underpin the ecology of Tonle Sap (Great Lake) in Cambodia, the management of flooding, acid sulphate soils and saltwater intrusion in the delta, and the need to control logging and deforestation throughout the basin. Infrastructure projects that isolate the river from its floodplain are of particular concern. The Mekong River Commission, established in 1995, provides a mechanism for shared management of the water resources of the Mekong River. Water is also used and managed at other levels within each riparian country. Governance of water in the Mekong Basin is a key challenge. This paper describes the current and potential uses of water in the Mekong Basin for irrigated agriculture, fish production, the generation of hydropower and environmental services. It examines the effects of current and proposed dams on the natural environment and on the sustainability of agriculture and fisheries. The paper also considers the effectiveness of the Mekong River Commission as an organisation enabling shared management of the basin’s water resources, looking particularly at governance challenges in a transboundary river basin that is subject to heavy development pressures.