The following research aims at understanding why states cooperate more than they fight over internationally shared natural resources. The debate on those issues has long been polarized between conflict- or cooperation-oriented contributions, respectively based on neo-Malthusian and Cornucopian scientific arguments. The puzzle of this research lies in the paradox between: the dominant pessimistic discourse, relayed by the media and public policy makers, which basically argues that those resources will lead to conflicts and even wars in the future; and the empirical reality, which supports a more optimistic outcome, with occurrences of cooperation largely overwhelming conflictive ones. Inspired by recent – and more nuanced – critical inputs on the matter, the research focuses on the case of transboundary water resources shared by three or more “riparian states” in order to answer the following research question: why do states rather cooperate over transboundary water resources?