Summary: In its review of lessons learned from four rounds of military base closures and realignments, GAO found that many neighboring communities have been able to absorb the economic losses stemming from closed bases. Several federal programs appear to have helped cushion the impact of closing bases on individuals and communities. However, the Defense Department (DOD), which projects billions of dollars in annual savings from closed bases, has yet to produce firm data on expected savings. Given the historical difficulty of closing bases, new legislation will be needed if there are to be future base closures. DOD has proposed that Congress authorize two additional rounds of military base closures and realignments. If future rounds are authorized, decisions will be needed on the number of rounds, when they should be held, and how they will relate to other legislation dealing with downsizing and restructuring DOD's laboratories and test and evaluation facilities. The outcome of future rounds could be improved by resolving, in advance, key organizational and policy issues, such as which military service will be responsible for which support functions and whether some facilities will be managed jointly. The Office of the Secretary of Defense will have to exercise strong leadership to overcome the services' long-standing parochialism and inability to agree on significant cross-service consolidations in common support areas.