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.

Tristan und Isolde, WWV 90, is an opera in three acts by Richard Wagner to a German libretto by the composer, based largely on the 12th-century romance Tristan and Iseult by Gottfried von Strassburg. It was composed between 1857 and 1859 and premiered at the Königliches Hoftheater und Nationaltheater in Munich on 10 June 1865 with Hans von Bülow conducting. Wagner referred to the work not as an opera, but called it "eine Handlung".