To introduce the topic of chemical agents, we discuss their place in the context of terrorist use of weapons of mass destruction, their recent uses on human populations, and the approach to national and international response. Despite international treaties and efforts to control the spread of chemical agents, these weapons remain a real threat. Both chemical agents and industrial hazardous materials can be used by terrorists. The public health system must be ready for chemical attack by having proper plans, infrastructure and supplies, and public health surveillance systems all in place. Improved and increased research in medical countermeasures, information sharing and coordination, education and training programs represent the key words to manage this emerging priority.