By analyzing 648 groups that existed between 1968 and 2006, this monograph examines how terrorist groups end. Its purpose is to inform U.S. counterterrorist efforts by understanding how groups have ended in the past and to assess implications for countering al Qa’ida. This monograph results from the RAND Corporation’s continuing program of self-initiated independent research. Support for such research is provided, in part, by donors and by the independent research and development provisions of RAND’s contracts for the operation of its U.S. Department of Defense federally funded research and development centers.