Decontamination involves the removal of or rendering inert any contaminant believed to be potentially harmful to a person or object. The contaminant may or may not be toxic; it may simply by an annoyance. Some believe that properly identifying a contaminant is essential to effective decontamination; however, regardless of the agent identified, water is the universal decontamination agent. The priority need to administer proper medical treatment to victims will, in all but a few cases, preclude complete agent identification prior to the beginning of the decontamination process. Still, the agent should be identified as soon as possible; and once identified, the incident commander can inform the decon officer, who will adjust the decon strategy as necessary. This article distinguishes "technical" decon from "medical" decon. "Technical" decon involves removing contaminants from inanimate objects such as vehicles, tools, suits, etc. "Medical" decon involves the administration of appropriate medical services for victims. Also discussed in the article are decontamination prioritization, the prioritizing of ambulatory victims for decontamination, operations in the "hot zone" (site of the highest concentration of contaminant), and ensuring that ample amounts of water are available for decontamination. In discussing methods of mass decontamination, the article advises that disrobing and showering is, in and of itself, decontamination. Showering is recommended whenever liquid transfer from clothing to skin is suspected. The use of water prior to disrobing may speed up the decontamination process and is generally recommended for any casualties who are contaminated with liquids. The article describes three decontamination systems developed by three fire and rescue departments. This is followed by profiles of commercially available contamination systems, most of which are mounted to or carried on special trailers that require transportation to and set up at the incident site. Finally, the article advises that evidence collection and environmental considerations should never have priority over the decontamination of any victims in incidents that may involve criminal behavior. 7 references