The Standard Generalized Markup Language (SGML) is a metalanguage in which one can define markup languages for documents. SGML is a descendant of IBM's Generalized Markup Language (GML), developed in the 1960s by Charles Goldfarb, Edward Mosher and Raymond Lorie (whose surname initials also happen to be GML). SGML should not be confused with the Geography Markup Language (GML) developed by the Open GIS Consortium; cf, or the Game Maker scripting language, GML.

SGML provides a variety of markup syntaxes that can be used for many applications. By changing the SGML Declaration one does not even need to use"angle brackets" although they are the norm, the so-called concrete reference syntax.

SGML was originally designed to enable the sharing of machine-readable documents in large projects in government, legal and the aerospace industry, which have to remain readable for several decades-a very long time in information technology. It has also been used extensively in the printing and publishing industries, but its complexity has prevented its widespread application for small-scale general-purpose use.