The Text Encoding Initiative is both an organization and an eponymous vocabulary and associated methodology for transcribing texts for the purpose of analysis, study, and the production of fac simile editions. It is widely used in the Digital Humanities.

The TEI vocabulary was originally intended always to be customized to particular academic projects. However, a core subset, TEI Lite, became popular. The TEI Consortium provides an extension mechanism, One Document Does It All (ODD), which simplifies making a customization of TEI, and in particular one that includes and combines specific “modules” such as one for drama or one for transcribing natural-language dictionaries.

The primary context for using TEI is academic text processing and study of texts. An advantage of using it in that context is the high level of expertise and availability of assistance from other academics, as well as tools