Hydrological changes such as variability in water availability, extreme events like floods and droughts or water pollution pose a serious challenge to effective management of internationally shared water resources – no matter whether they are induced by climate change, large infrastructure projects in the river basin or other forms of environmental change. To address these management challenges, many states have established transboundary River Basin Organization (RBOs). The purpose of this paper is to investigate the ability of such RBOs to respond to exogenous environmental and man-made changes by identifying institutional mechanisms and management practices that have been established by the respective institutions or their member states to react to transformations in the basins’ environment. Drawing on the literature of neoinstitutionalist theory and hydropolitics approaches, a comprehensive analytical framework is being developed. It consists of the following determinants of adaptation capacity: Membership structure, functional scope, decision-making mechanisms, data and information sharing, dispute-resolution mechanisms, finances and donor support. Subsequently, the framework is applied to two case studies, the Okavango and the Mekong River Basin. The paper concludes that the adaptation capacity of RBOs depends significantly on these factors, however, further research to quantify their respective impact and to test hypotheses on a larger number of cases is needed.