Chlorine gas was used as a warfare agent in World War I, and more recently in Iraq and Syria, but despite its potential toxicity, it is also widely used industrially and as a disinfectant and bleach. Chlorine is a strong oxidizing agent that hydrolyzes in water to form hydrochloric and hypochlorous acids. The respiratory tract is the primary target organ in humans and animals, and toxicity can be manifested as sensory irritation, pulmonary dysfunction and injury, and ultimately death. Human and animal studies have shown that chlorine toxicity is influenced more by exposure concentration than duration, is gender-independent, and increases with age, cigarette smoking, and preexisting respiratory conditions such as asthma and airway hyperreactivity. Current US workplace standards limit chlorine air concentration to 0.5 or 1 ppm for 15 min periods to prevent significant upper respiratory tract irritation. Treatment for chlorine inhalation is largely supportive, although animal studies are exploring the utility of various compounds for chlorine-specific treatment.