Taurine, or 2-aminoethanesulfonic acid, is an organic acid. It is also a major constituent of bile and can be found in the lower intestine and, in small amounts, in the tissues of many animals, including humans. Taurine is a derivative of the sulfur-containing (sulfhydryl) amino acid cysteine. Taurine is one of the few known naturally occurring sulfonic acids.

Taurine is named after the Latin Taurus, which means bull or ox, as it was first isolated from ox bile in 1827 by German scientists Friedrich Tiedemann and Leopold Gmelin. In the strict sense, it is not an amino acid, as it lacks a carboxyl group,but it is often called one, even in scientific literature. It does contain a sulfonate group and may be called an amino sulfonic acid. Small polypeptides have been identified which contain link, but to date no aminoacyl tRNA synthetase has been identified as specifically recognizing taurine and capable of incorporating it into a tRNA.