Tristan und Isolde (Tristan and Isolde, or Tristan and Isolda, or Tristran and Ysolt) is an opera, or music drama, in three acts by Richard Wagner to a German libretto by the composer, based largely on the romance by Gottfried von Strassburg. It was composed between 1857 and 1859 and premiered at the Königliches Hof- 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" (literally a drama, a plot or an action), which was the equivalent of the term used by the Spanish playwright Calderón for his dramas.