Benzene is a chemical compound with the molecular formula C6H6, composed of six carbon atoms joined in a planar hexagonal ring with one hydrogen atom attached to each. It is a colorless or light yellow liquid at room temperature with a sweet smell, and is highly flammable. Benzene is classed as a hydrocarbon because it contains only carbon and hydrogen atoms, and is a natural constituent of petroleum and one of the elementary petrochemicals. Due to the cyclic continuous pi bonds between the carbon atoms, benzene is classed as an aromatic hydrocarbon.

Benzene is widely used in the United States, ranking in the top 20 chemicals for production volume. It is used to make other chemicals, including plastics, resins, lubricants, rubbers, dyes, detergents, drugs, and pesticides. Benzene is also used as a solvent in the chemical and pharmaceutical industries, as a starting material and an intermediate in the synthesis of numerous chemicals, and in gasoline. It is produced naturally by volcanoes and forest fires, and is a natural component of crude oil, which is the main source of benzene produced today.

Benzene is highly toxic to humans, and exposure to high levels of benzene can cause cancer, particularly leukemia and other blood-based cancers. People can be exposed to benzene primarily by breathing air that contains the chemical, and workers in industries that produce or use benzene may be exposed to the highest levels of it. Other sources of exposure include tobacco smoke, gasoline fumes, motor vehicle exhaust, and industrial emissions. Benzene may also be found in glues, adhesives, cleaning products, paint strippers, and some types of medications.