In the decade since September 11, 2001, a terrorist attack using radiological materials-usually referred to as a “dirty bomb,” but actually encompassing other means of dispersal-has sometimes seemed inevitable. But terrorists have not yet carried out such an attack. Not only do many groups lack the motivation to engage in radiological terrorism, but these types of attacks also require technical, logistical, and financial means beyond those needed for terrorism using conventional methods. This article seeks to address technical questions associated with radiological terrorism. It first presents a summary of the commercially available radioactive sources, dispersal methods, and exposure pathways that could be deployed in a radiological attack. It then critically assesses the simulation-driven, open source research that has been done in the past ten years in the United States. The article goes on to note the estimated effects of a radiological attack according to these studies, with an emphasis on the motivations for, lessons derived from, and misconceptions or shortcomings contained in the various attack scenarios. Finally, the article draws conclusions and implications for the prevention and mitigation of radiological terrorism based on these studies and their respective limits, which mainly consist of technical, scope, and design limits or omissions, and suggests areas for further inquiry.