SIPRI Stockholm International Peace Research Institute is an independent institute for scientific research, which aims to further an understanding of the conditions for peaceful solutions to international conflicts and for a stable peace. Over the past twenty years, SIPRI has concentrated on problems ofarmaments, disarmament, and arms regulation. SIPRI is financed mainly by the Swedish Parliament. Its staff, the Governing Board, and the Scientific Council are international. The prospect of large reductions of nuclear weapons poses fundamental questions about the purpose of nuclear weapons. Why have some states chosen to acquire nuclear weapons? How - and why - have these decisions been maintained over time? Why have some states elected to approach, but not cross, thenuclear threshold? This book examines the commonalities and differences in political approaches to nuclear weapons both within and among three groups of states: nuclear, non-nuclear, and threshold. The chapters explore the evolution of thinking about nuclear weapons and the role these weapons play in nationalsecurity planning. The book transcends traditional East-West approaches to analysis of nuclear issues by giving equal prominence to the issues of nuclear proliferation and non-nuclearism. The book also provides a comprehensive analysis of how current approaches to nuclear weapons have evolved both within and amongthe countries under study.