It is very difficult to do justice to a subject as broad and complex as this in a period of an hour or two. I shall therefore limit myself to the most important aspects of the subject. My remarks in this seminar will consist of two parts, first, the political aspects of non-proliferation and second, some of the academical aspects of the subject. Let me start by giving some definitions, discussions of nuclear weapons and the motivation for using them, type of protection against such action, and U.S. policy and study program and the international situation. I will say a little also about reprocessing of nuclear fuel and its relation to the fuel supply problems and as well comment on the breeder reactor.