Toluene, also known as methylbenzene or phenylmethane is a clear water-insoluble liquid with the typical smell of paint thinners, reminiscent of the sweet smell of the related compound benzene. Toluene is an aromatic hydrocarbon that is used as an octane booster in fuel, as a solvent in paints, paint thinners, chemical reactions, rubber, printing, adhesives, lacquers, leather tanning, disinfectants, and to produce phenol and TNT. It is also used as a raw material for toluene diisocyanate, which is used in the manufacture of polyurethane foams.

The name toluene was derived from the older name toluol that refers to tolu balsam , an aromatic extract from the tropical American tree Myroxylon balsamum, from which it was first isolated.

Toluene occurs naturally at low levels in crude oil and usually produced in the process of making gasoline via a hydrogen reformer, in an ethylene cracker or making coke from coal. Final separation (either via distillation or solvent extraction) will take place in a BTX plant.

Inhaling of toluene fumes can be intoxicating, but in larger doses nausea-inducing. Chronic or frequent inhalation of toluene over long time periods leads to irreversible brain damage.