Hydro resources are provided by nature. The exploitation of such resources can generate significant economic rent to the owners. In the past, governments have usually claimed ownership of hydroelectric resources and passed on the rents to their state-owned utilities, which have used them to expand their systems or provide lower tariffs to their consumers. With the restructuring of the electric power sector in many countries, a more explicit consideration of hydroelectric rents is required. Moreover, hydropower resources are often owned by more than one party, or at least require cooperation between parties to develop them. In this context, the measurement and apportionment of hydropower rents between cooperating parties becomes important.This paper addresses some of the issues involved in cooperative development of water resources, especially for hydroelectric generation. It promotes a better understanding of the sources of the benefits and attempts to derive an analytical basis for discussions between cooperating parties.This volume will be of interest to hydropower resource earning countries, hydropower developers, and Bank staff.