Multireservoir operating policies are usually defined by rules that specify either individual reservoir desired (target) storage volumes or desired (target) releases based on the time of year and the existing total storage volume in all reservoirs. This paper focuses on the use of genetic search algorithms to derive these multireservoir operating policies. The genetic algorithms use real-valued vectors containing information needed to define both system release and individual reservoir storage volume targets as functions of total storage in each of multiple within-year periods. Elitism, arithmetic crossover, mutation, and en bloc replacement are used in the algorithms to generate successive sets of possible operating policies. Each policy is then evaluated using simulation to compute a performance index for a given flow series. The better performing policies are then used as a basis for generating new sets of possible policies. The process of improved policy generation and evaluation is repeated until no further improvement in performance is obtained. The proposed algorithm is applied to example reservoir systems used for water supply and hydropower.¿ 1997 American Geophysical Union