Lulu (written mostly in 1934, premièred incomplete in 1937) is an opera by the composer Alban Berg. The libretto was adapted by Berg himself from Frank Wedekind's plays Erdgeist (Earth Spirit, 1895) and Die Büchse der Pandora (Pandora's Box, 1904).

Berg first saw Die Büchse der Pandora in 1905 in a production by Karl Kraus, but did not begin work on his opera until 1929, after he had completed his other opera, Wozzeck. He worked steadily on the score until 1935, when the death of Manon Gropius, the daughter of Walter Gropius and Alma Mahler, prompted him to break off work to write his Violin Concerto.

Berg completed the violin concerto swiftly, but the time he spent on that meant he was unable to complete the opera before his death later in 1935. The following portions of the third and final act were fully scored: the first 268 bars; the instrumental interlude between scenes 1 and 2; and the finale of the opera, beginning with the monologue of Countess Geschwitz. (The last two of these passages comprise the fourth and fifth movements of the Lulu Suite which Berg compiled for concert performance.) The rest of the work remained in short score with indications of instrumentation for much of it.

Berg was able to hear the Symphonic Pieces in a BBC radio broadcast from the Queen's Hall, London on 20 March 1935, conducted by Adrian Boult and produced by Edward Clark. It was the first time he had ever heard any of the music of Lulu. He was not to hear these excerpts performed live until a concert in Vienna on 11 December, a fortnight before his death.

The opera was first performed by the Zurich Opera in an incomplete form in 1937. Erwin Stein made a vocal score of the whole of act 3 following Berg's death, and Helene Berg, Alban's widow, approached Arnold Schoenberg to complete the orchestration. Schoenberg at first accepted, but upon being sent copies of Berg's sketches he changed his mind, saying that it would be a more time-consuming task than he had thought. Helene subsequently forbade anybody else to complete the opera, and for over forty years only the first two acts could be given complete, usually with the act 3 portions of the Lulu Suite played in place of act 3. The last recording made of the original two-act version—Christoph von Dohnányi conducting the Vienna Philharmonic, with Anja Silja in the title role (Decca/London, recorded 1976 and released 1978)—presented it in this form.

Director Heinz Ruckert shot the silent film featured at the midpoint according to Berg's exacting specifications. The film wordlessly depicts Lulu's arrest, trial, incarceration, and ultimate liberation thanks to the cunning of the Countess Geschwitz. Like the music for this sequence (and the opera as a whole), the film has a palindromic structure. The original film is lost save for four stills which remain in the Zurich Stadtarchiv. Each successive production requires a new film to be shot with the stage actors. However, many recent productions omit the film altogether.