© 2018, Hacettepe University, Faculty of Pharmacy. All rights reserved.The use of “chemical warfare agents (CWA)” as mass destruction weapons first started in World war I. However, use of toxic agents in wars and in attack started in the first ages of written history. The threat of chemical weapons reached to important extents in the last part of the 20th century and became a current issue in the mass destructions and terrorist events. Therefore, nowadays and generally in the 21st century, it should be accepted that the chemical weapons take their part along with the conventional weapons and they have become most possible warfare and attack methods. Today the best way to defend against chemical and biological weapons is “preparedness”. Preparedness has two components: “knowledge” and “equipment”. Knowledge is provided by education. The counterparts of equipment are personnel, appliance, devices, organization and coordination. In this review, we will mainly focus on the history of chemical warfare agents, their toxicities and detections as well as the concept of “preparedness”.