The potential terrorist weapons that produce the most concern for many people are chemical agents, biological agents, radiological dispersal devices, and nuclear bombs. These weapon systems are collectively referred to as CBRNs. The psychological impact of these weapons is dependent upon the perception of the weapon and how it might be deployed. Some weapons potentially pose a much greater physical threat than conventional weapons (e.g., nuclear), but others weapons are probably comparable to conventional weapons (e.g., radiological dispersal devices). The terror value of these weapons, however, is often much greater than the terror produced by conventional weapons. Counter-measures and the treatment of casualties are also different for CBRNs than for conventional weapons.