How should the 'problem of order' associated with weapons of mass destruction be understood and addressed today? Have the problem and its solution been misconceived and misrepresented, as manifested by the problematic aftermath of the Iraq War? Has 9/11 rendered redundant past international ordering strategies, or are these still discarded at our own peril? These are the questions explored in this Adelphi Paper. It opens by focusing attention on the linked problems of enmity, power and legitimacy, which lie at the root of the contemporary problem of order. The Paper shows how the 'WMD order' that was constructed during and after the Cold War was challenged from various directions in the late 1990s and early 2000s. It shows how the growing disorder was a cause and effect of a potent 'double enmity' that arose in the US against both 'rogue states' and the international constitutionalism that had been espoused by previous US government and bound states to a common purpose. An ordering strategy that is imperious and places its main emphasis on counter-proliferation and the threat of preventive war cannot be successful. The recovery of order must entail the pursuit of international legitimacy as well as efficacy. It will require all states to accept restraint and to honour their mutual obligations.