Far from producing a new era of peace, tranquillity and respect for international law, the ending of the Cold War has fuelled fresh concerns about the proliferation of weapons of mass destruction. These anxieties mounted both during and after the Gulf War, and were compounded by the revelations of the UN inspectors in Iraq and the belated Russian admission that scientists in the former Soviet Union had been engaged in a covert biological weapons programme for some twenty years. This book examines the changing pattern both of incentives and of disincentives for such proliferation, including the utility of these weapons at state and sub-state levels. It also considers how other states should respond, assessing the achievements and limitations of arms and export controls, the evolving concept of deterrence, the debates about counter-proliferation policies and the problems in developing defences that will effectively counter an inherently dynamic phenomenon.