This study reviews the experience ofcooperation in five international river basins, focusing onthe perceptions of risks and opportunities by decisionmakers in countries responding to a specific prospect ofcooperation. For each basin, the analysis centered on'tipping points,' or periods in time whenpolicymakers in the countries involved were faced with acritical decision concerning water cooperation. This studyis primarily aimed at external development partners.Countries and individuals engaged in international watersissues may also find this study and reflections helpful inenhancing their knowledge and advancing their action withrespect to regional cooperation. There appear to be fivegeneral categories of risk perceived by decision makers.These risk categories were developed through a review ofliterature on international negotiation and cooperation. Ineach of the cases, the analysis focused on risks associatedwith these five broad categories, examining how these risksinfluenced decision makers and how the risks affected theoutcomes of negotiations.