Book excerpt: The making of policy for nuclear security requires a strong grasp of the associated technical matters. That grasp came naturally in the early decades of the nuclear era, when scientists and engineers were deeply engaged in policymaking. In more recent decades, the technical community has played a narrower role, one generally limited to implementing policies made by others. This narrower role has been accentuated by generational change in the technical community, as the scientists and engineers who conceived, built, and executed the programs that created the existing U.S. nuclear deterrent faded into history along with the long-term competition for technical improvements with the Soviet Union. There is thus today a clear need to impart to the new generation of nuclear policy experts the necessary technical context.That is the purpose of this paper. Specifically: to introduce a new generation of nuclear policy experts to the technical perspectives of a nuclear weapon designer, to explain the science and engineering of nuclear weapons for the policy generalist, to review the evolution of the U.S. approach to nuclear weapons design, to explain the main attributes of the existing U.S. nuclear stockpile, to explain the functions of the nuclear weapons complex, and how this all is integrated to sustain deterrence into the future.