This part of ISO 639 gives the general principles of language coding using the codes that are specified in the other parts of ISO 639 and their combination with other codes. Furthermore, this part of ISO 639 lays down guidelines for the use of any combination of the parts of ISO 639.

The terminology and general descriptions of this part of ISO 639 are intended to replace corresponding text of other parts of ISO 639 as relevant in future revisions.

Relevant metadata for the description of linguistic entities are also given, as a framework for databases of linguistic data to support the ISO 639 series of International Standards.