Water diplomacy needs institutional anchoring. International River Basin Organizations (RBOs) – being the result of diplomatic efforts by riparian states intending to create a framework for cooperation between themselves over shared water bodies – can provide such institutional anchors. RBOs ensure that agreements to cooperate are turned into a long-term commitment by riparian states to jointly manage shared water resources and, in turn, foster mutually beneficial cooperation over time. RBOs have been the subject of detailed examinations of their conceptual core, of their manifold functions, of their effectiveness in achieving their goals and so forth. However, the legal nature of these entities has so far received limited attention notwithstanding its significance in empowering RBOs to act as institutional anchors for water diplomacy. Legitimate questions arise, for instance, in relation to their legal personality, or lack thereof, or to matters such as immunities and privileges. This paper will review key legal aspects of RBOs and illustrate them with examples. A sound understanding of such issues is crucial to supporting fruitful discussions between state members about the legal design of an RBO in order to fulfill their particular needs in the context of water diplomacy.