For more than two decades, policymakers and academics have become steadily more concerned about the threat posed by WMD terrorism. This concern became even more acute in the wake of the March 20, 1995, sarin nerve agent attack on the Tokyo subway system by an apocalyptic millenarian religious groups known as Oumu (or Aum) Shinrikyo (Aum Supreme Truth), an event that has been described as the “first major sub-state use” of such a weapon (Cameron 1999b). Many experts argued that Aum’s blatant and indeed traumatic violation of long-standing societal taboos against the use of WMD by nonstate actors represented a “qualitative leap” that would soon inspire other terrorist groups to employ these weapons, whereas other specialists instead insisted that terrorists were likely to continue to rely on tried-and-true conventional weapons. As it turned out, neither of these positions was entirely warranted (Jenkins 1997). Although no significant spike in actual incidents of WMD terrorism has yet occurred, there are increasing indications that certain types of terrorist groups are planning WMD attacks and, more worrisome still, several apparent WMD plots have already been interdicted. There is therefore an urgent need to separate fact from fiction by examining, synthesizing, and critically evaluating the existing scholarly and policy-oriented literature that addresses WMD terrorism.