Transboundary cooperation on water as one aspect of good water governance will become increasingly important in the future. A global legal framework for cooperation on water exists ; yet it lacks binding force in many parts of the world. A variety of factors, ranging from hydrogeographical features of the basin to the socio-political realities and donor commitment, determine the likelihood and eventual shape of transboundary water cooperation. Cooperative institutional arrangements can be categorized according their purpose (single vs. multi-purpose cooperations) and their cooperation intensity, including a greater or lesser transfer of authority to a joint body. It must be recognized that cooperative institutional arrangements in this context cover an extremely broad spectrum, a fact that is not always clear because of the different uses of the term ‘institution’. And despite growing attention to and support for this topic, the institutional capacities of transboundary cooperative mechanisms are often weak compared to the challenges they face. The recent international workshop on Institutional Capacity Development in Transboundary Basins was the impetus for considering, in this paper, the requirements for capacity development to support cooperative mechanisms.