Since it has originated in its contemporary state in the XIXth century, the international law applicable to freshwater resources has expanded to embody the diversification of water-related activities. Its scope now includes issues like energy production, agricultural irrigation, access to drinking water, and environmental protection. Thus, the legal regime has evolved to respond to the challenges arising from the management and protection of freshwater resources at the universal, regional and basins levels. It goes without saying that cooperation among riparian States is necessary in the light of their hydraulic interconnectedness. In her book Cooperation in the Law of Transboundary Water Resources, Christina Leb, an Associate Member of the University of Geneva’s Platform for International Water Law, offers an extensive introduction into the legal developments of the principle of cooperation in international water law. The book focuses primarily on highlighting prevailing trends in treaty practice in order to provide an analysis of the evolution, current state and future trends of the rules of cooperation in the context of shared freshwater resources.