Eugene Onegin (Russian: Евгений Онегин, romanized: Yevgény Onégin, IPA: [jɪvˈɡʲenʲɪj ɐˈnʲeɡʲɪn] ^ⓘ), Op. 24, is an opera (designated as "lyrical scenes") in 3 acts (7 scenes), composed by Pyotr Ilyich Tchaikovsky. The libretto, organised by the composer himself, very closely follows certain passages in Alexander Pushkin's 1825–1832 novel in verse, retaining much of his poetry. Tchaikovsky's friend Konstantin Shilovsky contributed M. Triquet's verses in Act 2, Scene 1, while Tchaikovsky himself arranged the text for Lensky's arioso in Act 1, Scene 1, and almost all of Prince Gremin's aria in Act 3, Scene 1.

Eugene Onegin is a well-known example of lyric opera, to which Tchaikovsky added music of a dramatic nature. The story concerns a selfish hero who lives to regret his blasé rejection of a young woman's love and his careless incitement of a fatal duel with his best friend.

The opera was first performed in Moscow in 1879. There are several recordings of it, and it is regularly performed. The work's title refers to the protagonist.

In May 1877, the opera singer Yelizaveta Lavrovskaya spoke to Tchaikovsky about creating an opera based on the plot of Alexander Pushkin's 1825–1832 verse novel Eugene Onegin. Tchaikovsky felt that the novel wasn't particularly strong in plot – a dandy rejects a young country girl, she successfully grows into a worldly woman, he tries to seduce her but it is too late. The strength of the novel resided in its character development and social commentary, as well as in the beauty of its literary delivery. Soon after a sleepless night, Tchaikovsky came to embrace the idea. He created the scenarios in one night before starting the composition of the music.

Tchaikovsky, with some minor involvement by Konstantin Shilovsky, used original verses from Pushkin's novel and chose scenes that involved the emotional world and fortunes of his heroes, calling the opera "lyrical scenes." The opera is episodic; there is no continuous story, just selected highlights of Onegin's life. The composer finished the opera by January 1878.

Tchaikovsky worried whether the public would accept his opera, which lacked traditional scene changes. He believed that its performance required maximum simplicity and sincerity. With this in mind, he entrusted the first production to the students of the Moscow Conservatory. The premiere took place on 29 March (17 March O.S.) 1879 at the Maly Theatre, Moscow, conducted by Nikolai Rubinstein, with set designs by Karl Valts (Waltz). Whatever misgivings Tchaikovsky had, over the next century the public embraced the opera and it is frequently performed all over the world.

Two years later the first performance at the Bolshoi Theatre in Moscow took place on 23 January (11 January O.S.) 1881 with conductor Eduard Nápravník.

Outside Russia the initial reception was lukewarm, and it was slow to reach European cities, being seen as a Russian curiosity. The first performance outside Russia took place on 6 December 1888 in Prague, conducted by Tchaikovsky himself, although the rehearsals had been the responsibility of Adolf Čech. It was sung in Czech and translated by Marie Červinková-Riegrová.