This article examines the extent to which terrorist use of nuclear, chemical, and biological weapons poses a tangible threat to international security. In the literature on terrorism and weapons of mass destruction (WMD) some analysts have tended to exaggerate the scope of the threat and assumed that large-scale terrorist acts involving WMD are only 'a matter of time'. In short, there is a tendency among observers to converge on analogous assessments at the higher end of the threat spectrum. In this article I argue that although WMD terrorism remains a real prospect, the ease with which such attacks can be carried out has been exaggerated; acquiring WMD capabilities for delivery against targets is a lot more problematic for terrorists than is generally acknowledged in the literature. However, this is not to say that the possibility of such attacks can (or should) be ruled out. The rise of a 'new' brand of terrorism that operates across transnational networks and whose operations aim to inflict mass casualties, coupled with the destructive threshold crossed on 11 September 2001, mean that terrorist attacks using WMD will continue to be a realistic prospect in the future.