The Prose Tristan is an adaptation of the Tristan and Iseult story into a long prose romance, and the first to tie the subject entirely into the arc of the Arthurian legend. It was also the first major Arthurian prose cycle commenced after the widely popular Lancelot-Grail, which influenced especially the later portions of the Prose Tristan.

Tristan and Iseult, also known as Tristan and Isolde and other names, is a medieval chivalric romance told in numerous variations since the 12th century. Based on a Celtic legend and possibly other sources, the tale is a tragedy about the illicit love between the Cornish knight Tristan and the Irish princess Iseult. It depicts Tristan's mission to escort Iseult from Ireland to marry his uncle, King Mark of Cornwall. On the journey, Tristan and Iseult ingest a love potion, instigating a forbidden love affair between them.