Keywords Transboundary rivers Hegemony Asymmetry Two-level games Hydropolitics1 IntroductionWater connects, and transboundary rivers connect a host of actors in different states inmultiple ways. Riparian states can depend on each other for sea access, generating jointbenefits and minimising the losses from natural hazards. Yet, riparians can also use theriver to annoy, threaten, and damage each other by discharging wastewater into the basin orconstructing sufficient dams to store and regulate the river’s flow (Zawahri 2008). In anincreasingly interdependent world, we would expect a growing number of transboundaryriver treaties as states attempt to minimise the social, economic, and political lossesincurred from developing the basin and preventing unwelcome unilateral action. Suchattempts at cooperation may also lead to more integrated river basin management.Yet even when international water agreements are signed, it does not mean contractingstates are actually cooperating, and the lack of agreement does not mean riparian states arefighting. In other words, the presence of a treaty does not automatically translate intobehavioural altering cooperation. In the Iberian Peninsula and on the Mekong basin, forexample, relations remain conflictive despite some form of institutionalised cooperation.Thus, conflict and cooperation are ambiguous terms that tend to be used to describe howstates interact over their shared water resources. The objective of this special issue is totease out the dynamics of basin conflict and cooperation where power relations areasymmetric.