Aniline  is an organic compound with the formula C ₆ H ₅ NH ₂ . Consisting of a phenyl group attached to an amino group, aniline is the simplest aromatic amine. It is an industrially significant commodity chemical, as well as a versatile starting material for fine chemical synthesis. Its main use is in the manufacture of precursors to polyurethane, dyes, and other industrial chemicals. Like most volatile amines, it has the odor of rotten fish. It ignites readily, burning with a smoky flame characteristic of aromatic compounds.

Chemically, it is considered an electron-rich benzene derivative, and as a consequence, reacts rapidly in electrophilic aromatic substitution reactions. Likewise, it is also prone to oxidation: while freshly purified aniline is an almost colorless oil, exposure to air results in gradual darkening of the sample (to yellow or red) due to the formation of strongly colored, oxidized impurities. Aniline can be diazotized to give a diazonium salt, which can then undergo various nucleophilic substitution reactions.

Like other amines, aniline is a base (p K _aH  = 4.6) and nucleophile, although it is a weaker base and poorer nucleophile than structurally similar aliphatic amines.