The International Organization for Standardization (ISO) stipulated three-letter codes to identify languages. The relevant norms are the following:

• ISO 639-2 (1998): identifies some 400 languages,
• ISO 639-3 (2006) [supersedes ISO 639-2]: identifies all the known languages.

By ISO 639-3, a language code consists of three lower-case letters.

ISO 639-3 is essentially based on the SIL Ethnologue, ed. 14 (). It is anticipated in SIL Ethnologue, ed. 15 (2005).