Publisher Summary This chapter discusses the reservoir operation. Guidelines for operation of a reservoir have to be developed in the planning stage of a project. These are then refined on the basis of actual operational experience. Such schedules range from rigid rules, which are to be exactly followed to flexible guidelines that permit considerable advantage to the operator. Such schedules can be in graphical, tabular, or narrative form or a combination of these. Reservoir operation is an important component of water resources planning and management. After construction, detailed guidelines are given to the operator to enable him to take appropriate decisions. A reservoir operation policy specifies the amount of water to be released from storage at any time depending on the state of the reservoir, level of demands, and any information about the likely inflow to the reservoir. The operation problem for a single-purpose reservoir is to decide the releases to be made from the reservoir so that the benefits for that purpose are maximized. For a multipurpose reservoir, it is also required to optimally allocate the release among purposes. The complexity of the problem of reservoir operation depends on the extent to which the various intended purposes are compatible. If the purposes are compatible, less effort is needed for coordination.