Growing demands for water in many parts of the nation are fueling the search for new approaches to sustainable water management, including how best to store water. Society has historically relied on dams and reservoirs, but problems such as high evaporation rates and a lack of suitable land for dam construction are driving interest in the prospect of storing water underground. The National Research Council convened a committee to assess past experiences with managed underground water storage systems and to identify research priorities for development of future underground storage projects. The resulting report concludes that managed underground storage should be considered a valuable tool in a water manager's portfolio and recommends ways to address the unique challenges posed by managed underground storage systems through research and regulatory measures.