Résumé : The thesis explores the reasons why states cooperate rather than fight over transboundary water resources. Through a mixed-method research involving both quantitative and qualitative analytical tools, the research shows that states tend to cooperate with one another when (a multidimensional conceptualisation of) interstate power relations are more symmetric, amongst other power-asymmetry arguments. They also tend to cooperate more than others when there exist a high disparity in the level of development between riparian states, and when their relations are characterised by high levels of economic interdependence.