Iodine was discovered in May 1811 by the French chemist, Bernard Courtois, who manufactured potassium nitrate for Napoleon's armies. In Courtois' process calcium nitrate, isolated from nitre beds, was converted to potassium nitrate by means of potash from wood ashes. In order to conserve potash much of the nitrate was converted to sodium nitrate by means of crude ash which was obtained from kelp (seawood ashes). While washing the kelp with sulfuric acid to destroy certain impurities. Courtois noticed violet fumes which condensed and corroded his copper equipment. Properties of this new substance were investigated by F. Clement and J. B. Desormes and later by J. L. Gay-Lussac, who first recognized it as a new element and named it after the Greek word for violet.

Since its discovery, iodine has been a major factor in the advance of chemical technology. Its importance in the development of synthetic organic chemistry is exemplified by Hofmann's researches on the reactions of alkali halides with ammonia and the amines, and Williamson, Wurtz and Grignard, in the advent of the 19th century.