This Nuclear Posture Review provides a roadmap for implementing President Obama's agenda for reducing nuclear risks to the United States, our allies and partners, and the international community. As the President said in Prague last year, a world without nuclear weapons will not be achieved quickly, but we must begin to take concrete steps today. This NPR places the prevention of nuclear terrorism and proliferation at the top of the U.S. policy agenda, and describes how the United States will reduce the role and numbers of nuclear weapons. Efforts like the New Strategic Arms Reduction Treaty with Russia, the Nuclear Security Summit, our work to strengthen the nuclear nonproliferation regime, and a broader approach to deterrence are central elements of this strategy. At the same time, as long as nuclear weapons exist, the United States must sustain a safe, secure, and effective nuclear arsenal -- to maintain strategic stability with other major nuclear powers, deter potential adversaries, and reassure our allies and partners of our security commitments to them.