Although the political salience of nuclear disarmament has fallen dramatically since the end of the Cold War, the threat posed by nuclear weapons today remains at least as great as it was before 1989. The growing number of states either armed with or actively developing nuclear weapons programmes has placed existing control and monitoring frameworks under strain. In this article, Baroness Williams, a long time campaigner for multilateral nuclear disarmament, discusses the nature of today's nuclear threat and particularly the political challenge presented by states whose behaviour is not predictable. If further proliferation is to be prevented, the international community must renew its efforts at implementing a robust regime of control. The IAEA must be given the authority and the resources necessary to conduct inspections anywhere in the world without prior warning. At the same time, the world's nuclear states powers must begin genuine efforts at disarmament.