Fidelio is a German opera with spoken dialogue in two acts by Ludwig van Beethoven. It is Beethoven's only opera. The German libretto is byJoseph 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 for 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.

Two years prior to the opening scene, the nobleman Florestan has exposed or attempted to expose certain crimes of the nobleman Pizarro. In revenge, Pizarro has secretly imprisoned Florestan in the prison over which Pizarro is governor. The jailer of the prison, Rocco, has a daughter, Marzelline, and a servant (or assistant), Jaquino. Florestan's wife, Leonore, came to Rocco's door dressed as a boy seeking employment, and Rocco hired her. On orders, Rocco has been giving Florestan diminishing rations until he is nearly starved to death.