Toluene (/ˈtɒljuiːn/), also known as toluol (/ˈtɒljuɒl/), is an aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a CH3 group attached to a phenyl group. As such, its IUPAC systematic name is methylbenzene. Toluene is predominantly used as an industrial feedstock and a solvent.
As the solvent in some types of paint thinner, permanent markers, contact cement and certain types of glue, toluene is sometimes used as a recreational inhalant and has the potential of causing severe neurological harm.