Summary: NASA and the Defense Department run several types of aerospace test facilities, including wind tunnels and rocket engine test stands. Since the end of the Cold War, Congress has been appropriating less money for aerospace programs. In response to shrinking budgets and reductions in personnel, NASA and DOD agreed in 1995 to cooperate in performing essential aerospace testing. In 1996, the agencies suggested establishing joint working groups to assess and make recommendations on investments and other issues. This report reviews efforts by NASA and DOD since then to develop a national perspective on aerospace test facilities. GAO discusses (1) the extent to which NASA/DOD working groups on major test facilities have been operating on a regular basis, (2) NASA's and DOD's actions in response to a future need to test an engine for new Air Force rockets, (3) whether NASA and DOD prepared a congressionally required joint plan on rocket propulsion test facilities, and (4) whether NASA and DOD are implementing a DOD assessment team's recommendation to jointly manage certain aeronautical test facilities with NASA.