The Swan of Tuonela (Tuonelan joutsen) is an 1895 tone poem by the Finnish composer Jean Sibelius. It is part of the Lemminkäinen Suite (Four Legends from the Kalevala), Op. 22, based on the Kalevala epic of Finnish mythology.

The tone poem is scored for a small orchestra of cor anglais, oboe, bass clarinet, two bassoons, four horns, three trombones, timpani, bass drum, harp, and divided strings. The cor anglais is the voice of the swan, and its solo is perhaps the best known cor anglais solo in the orchestral literature. The music paints a gossamer, transcendental image of a mystical swan swimming around Tuonela, the island of the dead. Lemminkäinen, the hero of the epic, has been tasked with killing the sacred swan; but on the way, he is shot with a poisoned arrow and dies. In the next part of the story he is restored to life.

The Swan of Tuonela was originally composed in 1893 as the prelude to a projected opera called The Building of the Boat. Sibelius revised it two years later, making it the second section of his Lemminkäinen Suite of four tone poems, which was premiered in 1896. He further revised the piece two times, once in 1897 and again in 1900. Sibelius left posterity no personal account of his writing of the tone poem, and its original manuscript no longer exists. (When it actually disappeared is unknown.) The work was first printed by the publishing firm of K.F. Wasenius in Helsingfors (Helsinki), Finland, in April 1901. The German firm Breitkopf & Hartel also published it in Leipzig in 1901.

Walt Disney had his studio staff do a fair amount of work on this as a segment for a planned sequel to his 1940 film, Fantasia. It was developed as a storyboard but was never animated.

A well known excerpt from the piece is used as introductory music to the BBC radio production of Lost Horizon.