Orpheus in the Underworld and Orpheus in Hell are English names for Orphée aux enfers (French: [ɔʁfe oz‿ɑ̃fɛʁ]), a comic opera with music by Jacques Offenbach and words by Hector Crémieux and Ludovic Halévy. It was first performed as a two-act "opéra bouffon" at the Théâtre des Bouffes-Parisiens, Paris, on 21 October 1858, and was extensively revised and expanded in a four-act "opéra féerie" version, presented at the Théâtre de la Gaîté, Paris, on 7 February 1874.

The opera is a lampoon of the ancient legend of Orpheus and Eurydice. In this version Orpheus is not the son of Apollo but a rustic violin teacher. He is glad to be rid of his wife, Eurydice, when she is abducted by the god of the underworld, Pluto. Orpheus has to be bullied by Public Opinion into trying to rescue Eurydice. The reprehensible conduct of the gods of Olympus in the opera was widely seen as a veiled satire of the court and government of Napoleon III, Emperor of the French. Some critics expressed outrage at the librettists' disrespect for classic mythology and the composer's parody of Gluck's opera Orfeo ed Euridice; others praised the piece highly.

Orphée aux enfers was Offenbach's first full-length opera. The original 1858 production became a box-office success, and ran well into the following year, rescuing Offenbach and his Bouffes company from financial difficulty. The 1874 revival broke records at the Gaîté's box-office. The work was frequently staged in France and internationally during the composer's lifetime and throughout the 20th century. It is one of his most often performed operas, and continues to be revived in the 21st century.

In the last decade of the 19th century the Paris cabarets the Moulin Rouge and Folies Bergère adopted the music of the "Galop infernal" from the culminating scene of the opera to accompany the can-can, and ever since then the tune has been popularly associated with the dance.

Between 1855 and 1858 Offenbach presented more than two dozen one-act operettas, first at the Bouffes-Parisiens, Salle Lacaze, and then at the Bouffes-Parisiens, Salle Choiseul. The theatrical licensing laws then permitted him only four singers in any piece, and with such small casts, full-length works were out of the question. In 1858 the licensing restrictions were relaxed, and Offenbach was free to go ahead with a two-act work that had been in his mind for some time. Two years earlier he had told his friend the writer Hector Crémieux that when he was musical director of the Comédie-Française in the early 1850s he swore revenge for the boredom he suffered from the posturings of mythical heroes and gods of Olympus in the plays presented there. Cremieux and Ludovic Halévy sketched out a libretto for him lampooning such characters. By 1858, when Offenbach was finally allowed a large enough cast to do the theme justice, Halévy was preoccupied with his work as a senior civil servant, and the final libretto was credited to Crémieux alone. Most of the roles were written with popular members of the Bouffes company in mind, including Désiré, Léonce, Lise Tautin, and Henri Tayau as an Orphée who could actually play Orpheus's violin.

The first performance took place at the Salle Choiseul on 21 October 1858. At first the piece did reasonably well at the box-office but was not the tremendous success Offenbach had hoped for. He insisted on lavish stagings for his operas: expenses were apt to outrun receipts, and he was in need of a substantial money-spinner. Business received an inadvertent boost from the critic Jules Janin of the Journal des débats. He had praised earlier productions at the Bouffes-Parisiens but was roused to vehement indignation at what he maintained was a blasphemous, lascivious outrage – "a profanation of holy and glorious antiquity". His attack, and the irreverent public ripostes by Crémieux and Offenbach, made headlines and provoked huge interest in the piece among the Parisian public, who flocked to see it. In his 1980 study of Offenbach, Alexander Faris writes, "Orphée became not only a triumph, but a cult." It ran for 228 performances, at a time when a run of 100 nights was considered a success. Albert Lasalle, in his history of the Bouffes-Parisiens (1860), wrote that the piece closed in June 1859 – although it was still performing strongly at the box-office – "because the actors, who could not tire the public, were themselves exhausted".

In 1874 Offenbach substantially expanded the piece, doubling the length of the score and turning the intimate opéra bouffon of 1858 into a four-act opéra féerie extravaganza, with substantial ballet sequences. This version opened at the Théâtre de la Gaîté on 7 February 1874, ran for 290 performances, and broke box-office records for that theatre. During the first run of the revised version Offenbach expanded it even further, adding ballets illustrating the kingdom of Neptune in Act 3 and bringing the total number of scenes in the four acts to twenty-two.

A spoken introduction with orchestral accompaniment (Introduction and Melodrame) opens the work. Public Opinion explains who she is – the guardian of morality ("Qui suis-je? du Théâtre Antique"). She says that unlike the chorus in Ancient Greek plays she does not merely comment on the action, but intervenes in it, to make sure the story maintains a high moral tone. Her efforts are hampered by the facts of the matter: Orphée is not the son of Apollo, as in classical myth, but a rustic teacher of music, whose dislike of his wife, Eurydice, is heartily reciprocated. She is in love with the shepherd, Aristée (Aristaeus), who lives next door ("La femme dont le coeur rêve"), and Orphée is in love with Chloë, a shepherdess. When Orphée mistakes Eurydice for her, everything comes out, and Eurydice insists they abandon the marriage. Orphée, fearing Public Opinion's reaction, torments his wife into keeping the scandal quiet using violin music, which she hates ("Ah, c'est ainsi").