Arms control and nonproliferation efforts are two of the tools that have occasionally been used to implement U.S. national security strategy. Although some believe these tools do little to restrain the behaviour of U.S. adversaries, while doing too much to restrain U.S. military forces and operations, many other analysts see them as an effective means to promote transparency, ease military planning, limit forces, and protect against uncertainty and surprise. Arms control and nonproliferation efforts have produced formal treaties and agreements, informal arrangements, and cooperative threat reduction and monitoring mechanisms. The pace of implementation for many of these agreements slowed during the Clinton Administration, and the Bush Administration usually preferred unilateral or ad hoc measures to formal treaties and agreements to address U.S. security concerns. The Obama Administration resumed bilateral negotiations with Russia and pledged its support for a number of multilateral arms control and nonproliferation efforts, but succeeded in negotiating only a few of its priority agreements. This book summarises cooperative activities conducted during the full 20 years of U.S. threat reduction and nonproliferation assistance.