Building on the interdisciplinary work of interactional theory of law: inspired by the insights from the constructivism theory in international relations (IR) and the practice theory of the legal theory of Lon Fuller, the thesis investigates the role of legal rules in the processes of regime development and peaceful settlement of disputes in shared river basins. Analysis in the thesis, through its methodological approach and analytical frameworks, illustrates how legal rules are influential in defining behaviours (of actors) and outcomes in those processes in the shared river basins, but not necessarily through the creation of ‘predictable rules' and ‘institutional structures' as most IR scholars or positivist lawyers speculate. Ultimately, the thesis offers an opportunity to reassess the role of legal rules and provide for their contributions in those processes in the shared river basins using the four selected case-studies of the shared river basins of Nile, Mekong, Indus, and Jordan.