The most effective means of defending against chemical warfare agents, whether in war or as result of terror, are by use of primary and secondary prevention. The main goal of medical prevention programs is to minimize human loss by reducing the number of casualties, by teaching advanced medical programs in order to assure a proper response, and to develop new and effective countermeasures. The toxicity, medical management, characteristic diagnostic signs, and treatment of casualties with vesicant, blood, choking and incapacitating agents are described. The importance of improved research and learning processes for medical and emergency personnel as well as of military nuclear, biological and chemical (NBC) unit preparedness in the chemical agent field are emphasized.