The Strategic Defense Initiative (SDI) to develop a ballistic missile defense (BMD) system has both short-range and long-range risks as well as potential benefits. For the most part, however, strategic, technological, and political issues relevant to SDI have been analyzed in isolation from one another. This book provides a more inclusive framework for assessing the possible development and deployment of a BMD system by the United States or the Soviet Union. Contributors discuss the risks for arms race stability, probable reactions of the Soviet Union to any U.S. space-based defense system, and implications for the stability of extended deterrence commitments to NATO European allies. They also evaluate Soviet research and development programs in missile defense that must be considered in any extrapolation of the requirements for U.S. deterrence in the next several decades.