The threat of nuclear weapons did not fade away with the collapse of the Soviet Union. Rather, the geo-political disorders of the post-Cold-War era and the rise of global terrorism have ensured that they remain conspicuously present on the world stage as a serious international concern. With the eight or nine nuclear powers maintaining about 27,000 nuclear weapons in their arsenals to this day, it is clear that they are here to stay for the foreseeable future. The primary mission of these nuclear forces has been and remains deterrence, the fear of reprisal. Using plain language rather than policy jargon, this historically-focused book shows how nuclear deterrence has worked rather than how theorists say it should work. It then shows how nuclear proliferation threatens to create a far more complicated international situation as the number of states with nuclear deterrents grows. By drawing on a wide array of new sources from international archives and the latest in international scholarship, the authors put some of the most important and enduring problems of nuclear deterrence over the past sixty years into global context. They take a fresh look at how nuclear weapons policy has been made, finding that it often has had surprisingly little to do with what works and what does not. By studying in depth how governments have confronted and dealt with some of the most important issues in nuclear weapons policy, they find that the making of policy is a complex, fluid bargaining process subject to the tides of politics, budgets, threat perception, ideology, technology, parochial service rivalries, flawed information, and sometimes just plain wishful thinking.