The reaction of a leather to a dye depends on the former's many intrinsic and acquired characteristics. The selection of a dye depends on the tannage and whether a surface dyeing is required (e.g. for shoe uppers) or if more penetration is needed (e.g. clothing or upholstery leather). Acid dyes, reactive dyes; and occasionally disperse dyes have been long used. The first dyes developed for leather were produced in 1911. In the 1920's, chrome leather was usually dyed with acid wool dyes, direct dyes and nigrosines. Metal-complex dyes might be used for glazed kid and gloves. Vegetable-tanned leathers were mainly brush-dyed using low-molecular weight wool dyes and cationic dyes. Diazotisation for producing blacks on suede was introduced around 1928. Only 5% of leather dyes were neither brown or black. Dual demand for dye penetration and covering power was met with mixtures of acid dyes and direct dyes. During the 1930's many new processes failed to improve leather dyeing. The most important achievement in the 1940's was the development of 1: 2 metal complex dyes which became popular in the 1960's when aniline leather demanded covering and light-fast dyeings on retanned leathers. The most promising development overall was probably that of reactive dyes. Current trends and goals are discussed, as well as leather dyeing auxiliaries (additives). Finally, the theory of leather dyeing and dye properties and fastness properties are explained. There are 116 references in this highly technical article.