Pumped storage hydroelectric projects provide an economic way of meeting peak energy needs in electric power systems. Types and locations of pumped storage projects and their basic engineering and operations are described together with the biological impacts common as well as unique to this form of power generation. The rapid increase in the number of pumped storage projects during the last 16 years and projected future construction indicate a serious need for expanded studies to provide for better design features and reduced environmental damage. Biological studies underway and those needed are described and discussed.