"Le cygne", pronounced [lə siɲ], or "The Swan", is the 13th and penultimate movement of The Carnival of the Animals by Camille Saint-Saëns. Originally scored for solo cello accompanied by two pianos, it has been arranged and transcribed for many instruments but remains best known as a cello solo.

The piece is in 6/4 (time signature), with a key signature of G major and a tempo marking andantino grazioso. The slow cello melody is accompanied by almost constant broken chord figurations on the pianos. When performed as a separate movement, not in the context of The Carnival, "The Swan" is frequently played with accompaniment on only one piano.

This is the only movement from The Carnival of the Animals that the composer allowed to be played in public during his lifetime. He thought the remaining movements were too frivolous and would damage his reputation as a serious composer.

"Le cygne" illustrates the fleeting nature of beauty with its interpretation of the legend of the "swan song": A popular belief among the ancient Greeks, who regarded the swan as among the most beautiful of animals, was that the mute swan is silent until its final moments of life, during which it sings the most beautiful of all birdsongs.

In the 1890s, Louis van Waefelghem arranged Le cygne for Viola or Viola d'amore accompanied by piano. This adaptation was subsequently published by the French music publisher Durand (publisher) in 1895. Around the same time, pianist Leopold Godowsky created a well-known free transcription for solo piano, adding to the piece’s growing popularity.

In a notable 20th-century interpretation, a young Gary Karr, at just 20 years old, performed the melody on double bass in Leonard Bernstein's recording of the work with the New York Philharmonic. The piece has also been interpreted vocally; soprano Montserrat Caballé recorded a version in which she vocalizes portions of the melody, supported by piano accompaniment.

The Thereminist Clara Rockmore brought the piece into the realm of Electronic music in the early 20th century, performing it on theremin with piano accompaniment by her sister, Nadia Reisenberg. Owing to its gentle tempo and smooth, Legato phrasing, Le cygne is well-suited to the expressive capabilities of the theremin. As a result, it has become a staple of the instrument’s repertoire, often performed alongside other lyrical works such as Sergei Rachmaninoff's Vocalise (Rachmaninoff) and Jules Massenet's Méditation from Thaïs.

In 1995, Euphonium soloist Steven Mead arranged Le cygne for euphonium and piano, transposing it to the key of E-flat major. The piece has also inspired popular and contemporary interpretations. Italian songwriter Tony Renis wrote lyrics for a version titled Notte Stellata (The Swan), featured on the debut album of the pop-opera trio Il Volo. In 2021, the Italian jazz group No Trio for Cats offered a reinterpretation under the title O Cisne de Janeiro, giving the piece a jazz-infused character. Additionally, an upbeat, accelerated version of Le cygne was produced for inclusion in the video game Gran Turismo 7, introducing the work to a new generation of listeners through digital media.