Agent Orange is a chemical herbicide and defoliant, one of the tactical uses of Rainbow Herbicides. It was notably used by the U.S. military as part of its herbicidal warfare program, Operation Ranch Hand,^[1] during the Vietnam War from 1962 to 1971.^[2] The U.S. was strongly influenced by the British who used Agent Orange during the Malayan Emergency. Primarily a mixture of equal parts of two herbicides, 2,4,5-T and 2,4-D, it contained trace amounts of 2,3,7,8-TCDD, a dioxin compound established as a carcinogen and persistent organic pollutant.

Agent Orange was produced in the United States beginning in the late 1940s and was used in industrial agriculture, and was also sprayed along railroads and power lines to control undergrowth in forests. During the Vietnam War, the U.S. military procured over 20,000,000 U.S. gal (76,000,000 L; 17,000,000 imp gal). Nine chemical companies produced it, including Dow Chemical Company and Monsanto Company.^[3]

Agent Orange exposure is linked to increased rates of birth defects, malignancies, cardiovascular diseases, and diabetes.^[4] The science on the causality between exposure and health problems remains incomplete.^[5][4] The U.S. government has documented cases of leukemia, Hodgkin's lymphoma, and various kinds of cancer in exposed U.S. veterans, but not concluded a causal relationship or a plausible biological carcinogenic mechanism.^[6] The U.S. Centers for Disease Control and Prevention identified an increase in the rate of birth defects of the children of exposed U.S. veterans.^[7][8]

The impact of Agent Orange in Vietnam includes health and ecological effects. The government of Vietnam says that up to four million people in Vietnam were exposed to the defoliant, and as many as three million people have suffered illness because of Agent Orange,^[9] while the Vietnamese Red Cross estimates that up to one million people were disabled or have health problems as a result of exposure to Agent Orange.^[10] The government of Vietnam defined victims of Agent Orange by looking at where they live, their family history, and if the health problems have been linked to Agent Orange.^[5] The U.S. government has described these figures as unreliable.^[11]

Agent Orange has also caused enormous environmental damage in Vietnam. This has been described by numerous lawyers, historians and other academics as ecocide.^[17] Over 7,700,000 acres (3,100,000 ha) or 12,000 sq mi (31,000 km²) of tropical forest were defoliated. Defoliants eroded tree cover and seedling forest stock, making reforestation difficult in numerous areas. Animal species diversity is sharply reduced in contrast with unsprayed areas.^[18][19]

The use of Agent Orange in Vietnam resulted in numerous legal actions. The United Nations ratified General Assembly Resolution 31/72 in 1976 and the Environmental Modification Convention in 1977. Lawsuits filed on behalf of both U.S. and Vietnamese veterans sought compensation for damages.