A markup language is a set of annotations to text that describe how it is to be structured, laid out, or formatted. Markup languages have been in use for centuries, and in recent years have also been used in computer typesetting and word-processing systems.

A well-known example of a markup language in use today in computing is HyperText Markup Language (HTML), one of the protocols of the World Wide Web. HTML follows some of the markup conventions used in the publishing industry in the communication of printed work between authors, editors, and printers.