Fidelio (Op. 72) is a German opera with spoken dialogue in two acts by Ludwig van Beethoven. It is his only opera. The German libretto is by Joseph Sonnleithner from the French of Jean-Nicolas Bouilly, which had been used for the 1798 opera Léonore, ou L’amour conjugal by Pierre Gaveaux, and the 1804 opera Leonora by Ferdinando Paer (a score of which was owned by Beethoven). The opera tells how Leonore, disguised as a prison guard named "Fidelio", rescues her husband Florestan from death in a political prison.

Bouilly's scenario fits Beethoven's aesthetic and political outlook: a story of personal sacrifice, heroism and eventual triumph (the usual topics of Beethoven's "middle period") with its underlying struggle for liberty and justice mirroring contemporary political movements in Europe.

As elsewhere in Beethoven's vocal music, the music is not especially kind to the singers. The principal parts of Leonore and Florestan, in particular, require great vocal skill and endurance in order to project the necessary intensity, and top performances in these roles attract admiration.

Some notable moments in the opera include the "Prisoners' Chorus", an ode to freedom sung by a chorus of political prisoners, Florestan's vision of Leonore come as an angel to rescue him, and the scene in which the rescue finally takes place. The finale celebrates Leonore's bravery with alternating contributions of soloists and chorus.