This volume appears at a time when the prospects for banishing the threat of nuclear annihilation are brighter than at any time since the first atomic device exploded over the desert at Alamogordo. The last few years have seen an ex- traordinary change in the climate of East-West relations. The programme of political and economic reform which President Gorbachev initiated in the Soviet Union and which is now spreading throughout most of Eastern Europe has been parallelled by serious efforts to reach agreement on measures for conventional and nuclear disarmament. This has led to new hope that international peace and security can at last be built upon the firm foundation of justice, respect for in- ternational law and a determination to approach problems in a spirit of genuine co-operation rather than one of distrust and confrontation. This new climate encourages us in the belief that the obvious common sense of preventing the further spread of nuclear weapons will come to be shared by all nations. At the same time, we have to recognize two very disturbing facts, which imply that there can be no slackening of our efforts to strengthen the non-proliferation regime.