Although comprising only a tiny proportion of all terrorist plots and attacks, the prospect of terrorists employing chemical, biological, radiological, or nuclear (CBRN) weapons has raised substantial concerns among both policymakers and the general public. While CBRN terrorist events do represent a real, asymmetric threat (with at least 558 incidents recorded in extant databases), most of these incidents would not constitute the use of genuine weapons of mass destruction (WMD). This is because, to form a viable weapon, the toxic chemical, biological pathogen, hazardous radioisotope, or fissile material must be combined with an effective delivery system; as the scale of the intended effects of such a weapon increases, so generally does its sophistication and the difficulty of acquiring or producing it. The threat of CBRN terrorism can be parsed into a consideration of both the motivations underlying its pursuit and the capabilities required to successfully deploy a CBRN weapon. A wide variety of factors can prompt terrorists to pursue a CBRN weapon. These can be usefully categorized into ideological or psychological drivers, operational and instrumental purposes, and organizational motives. At the same time, while terrorists can conceivably acquire a CBRN capability via state or nonstate sponsors, theft, or purchase, the most likely avenue is internal development of a weapon or an attack on a nuclear, chemical, or biological facility. Historically, there have been over 200 actual uses by terrorists of CBRN agents, with chemical incidents being the most common type. Most incidents have not resulted in many casualties, although there are a handful of mass-casualty incidents of CBRN terrorism. Past perpetrators reflect a diverse array of ideologies and have selected a wide range of delivery methods. Yet, past trends may not be a reliable indicator of the future threat. While low-end CBRN terrorism events will likely continue to predominate, and the COVID-19 pandemic is unlikely to appreciably increase the threat of bioterrorism, emerging technologies that facilitate acquisition efforts and the precedent set by groups like the Islamic State indicate that the potential for CBRN terrorism to result in a genuine WMD event will persist and might even increase over time. Therefore, while authorities must be careful not to exaggerate or amplify the threat of CBRN terrorism, CBRN terrorism is a phenomenon that requires continued attention, with efforts to prevent it that remain commensurate with the extant level of the threat.
Binder, Markus K., and Gary A. Ackerman. 2023. "CBRN Terrorism." Oxford Research Encyclopedia of International Studies (February). https://doi.org/10.1093/acrefore/9780190846626.013.706.