81) is a German grand heroic-romantic opera by Carl Maria von Weber, first performed at the Theater am Kärntnertor in Vienna on 25 October 1823.

[1] Though acknowledged as one of Weber's most important operas, the work is rarely staged because of the weak libretto by Helmina von Chézy (who, incidentally, was also the author of the failed play Rosamunde, for which Franz Schubert wrote music).

Only the overture, an outstanding example of the early German Romantic style (heralding Richard Wagner), is regularly played today.

Like Schubert's lesser-known Alfonso und Estrella, of the same time and place (Vienna, 1822), Euryanthe parts with the German Singspiel tradition, adopting a musical approach without the interruption of spoken dialogue characteristic of earlier German language operas such as Mozart's Die Zauberflöte, Beethoven's Fidelio, and Weber's own Der Freischütz.

Mahler realised the weaknesses of the libretto and the absurdities of the plot; in particular, in the third act, the ludicrously implausible meeting of all the characters in the middle of a rocky waste, a scene which he always alluded to as 'the merry folk reunited'.

[5] The composer and musicologist Donald Francis Tovey regarded Euryanthe as musically superior to Wagner's better-known opera Lohengrin (whose plot and music echo Euryanthe in several respects, especially with regard to the use of Leitmotiv technique) and made a new performing version, while Arturo Toscanini conducted the La Scala premiere in 1902.

Grove notes Weber's use of chromaticism to depict the evil characters, the fine orchestration, and the careful blend of recitative, arioso and set piece.

In a hall of the palace of King Louis VI of France in Prémery, the count sings the praises of his promised bride (who is not present).

Adolar's sister Emma had lost her lover in battle, and had killed herself by drinking poison from a ring (the 'ghost' music from the overture is heard).

Euryanthe, who has been praying each night at Emma's tomb, had promised Adolar to keep this secret, and, too late, she repents having told it to Eglantine.

Euryanthe longs for death, but the king and his hunters arrive on the scene, and she recounts the story of her woe and the treachery of Eglantine.

Meanwhile, Eglantine has become engaged to Lysiart, and the wedding is about to take place in the Castle of Nevers (no longer in Adolar's possession), when she is stricken with remorse.