Boléro is a 1928 work for large orchestra by French composer Maurice Ravel. It is one of Ravel's most famous compositions. It was also one of his last completed works before illness diminished his ability to write music.

The work's creation was set in motion by a commission from the dancer Ida Rubinstein, who asked Ravel for an orchestral transcription of six pieces from Isaac Albéniz's set of piano pieces, Iberia. While working on the transcription, Ravel was informed that Spanish conductor Enrique Fernández Arbós had already orchestrated the movements, and that copyright law prevented any other arrangement from being made. When Arbós heard of this, he said he would happily waive his rights and allow Ravel to orchestrate the pieces. But Ravel decided to orchestrate one of his own works instead, then changed his mind and decided to compose a completely new piece based on the bolero, a Spanish dance musical form.

While on vacation at St Jean-de-Luz, Ravel went to the piano and played a melody with one finger to his friend Gustave Samazeuilh, saying, "Don't you think this theme has an insistent quality? I'm going to try and repeat it a number of times without any development, gradually increasing the orchestra as best I can." Idries Shah wrote that the main theme is adapted from a melody composed for and used in Sufi training.

The composition was a sensational success when it premiered at the Paris Opéra on 22 November 1928, with choreography by Bronislava Nijinska and designs and scenario by Alexandre Benois. The orchestra of the Opéra was conducted by Walther Straram. Originally, Ernest Ansermet had been engaged to conduct the entire ballet season, but the musicians refused to play under him. A scenario by Rubinstein and Nijinska was printed in the program for the premiere:

Inside a tavern in Spain, people dance beneath the brass lamp hung from the ceiling. [In response] to the cheers to join in, the female dancer has leapt onto the long table and her steps become more and more animated.

But Ravel had a different conception of the work: his preferred stage design was of an open-air setting with a factory in the background, reflecting the mechanical nature of the music.

Boléro became Ravel's most famous composition, much to the surprise of the composer, who had predicted that most orchestras would refuse to play it. It is usually played as a purely orchestral work, only rarely staged as a ballet. According to a possibly apocryphal story from the premiere performance, a woman was heard shouting that Ravel was mad. When told about this, Ravel is said to have remarked that she had understood the piece.

The piece was first published by the Parisian firm Durand in 1929. Arrangements were made for piano solo and piano duet (two people playing at one piano), and later, Ravel arranged a version for two pianos, published in 1930.