This joint U.S. Department of Defense/U.S. Department of Energy report discusses nuclear weapons issues for the 21st Century. The report draws on policies from both current and prior administrations to address current and future challenges. The following is taken from the report: "In July 2007, along with Secretary of State Condoleezza Rice, we issued a statement that summarized the need for maintaining a credible U.S. nuclear deterrent and urged bipartisan Congressional support for the Reliable Replacement Warhead program. This paper, National Security and Nuclear Weapons in the 21st Century, expands on the July 2007 statement by addressing in greater detail the considerations behind U.S. requirements for nuclear weapons. The paper also describes the relationship among strategic nuclear force structure, the stockpile of nuclear warheads, and the nuclear warhead research and production infrastructure. We believe the logic presented here provides a sound basis on which this and future administrations can consider further adjustments to U.S. nuclear weapons policy, strategy, and force structure. Many of the policy issues and strategic capabilities discussed in this paper are based on the December 2001 Nuclear Posture Review and represent continuity with decisions made by prior administrations. For example, the Clinton Administration developed the 'lead and hedge' strategy as a way to reduce the size of the deployed strategic nuclear force, while also ensuring that the United States would be able to respond to future challenges that could be more stressing than estimated at that time. Under this strategy the United States would take the 'lead' in nuclear reductions, but would 'hedge' through an inventory of non-deployed nuclear warheads and a force structure capable of deploying those warheads. The current administration seeks to build on that approach by relying, over time, more heavily on a responsive nuclear weapons design and manufacturing infrastructure to manage risk, and less on an inventory of non-deployed warheads."