Twenty Thousand Leagues Under the Sea: A World Tour Underwater is a classic science fiction adventure novel by French writer Jules Verne.

The novel was originally serialized from March 1869 through June 1870 in Pierre-Jules Hetzel's fortnightly periodical, the Magasin d'education et de recreation.

A deluxe octavo edition, published by Hetzel in November 1871, included 111 illustrations by Alphonse de Neuville and Edouard Riou.

The book was widely acclaimed on its release and remains so; it is regarded as one of the premiere adventure novels and one of Verne's greatest works, along with Around the World in Eighty Days and Journey to the Center of the Earth.

Its depiction of Captain Nemo's underwater ship, the Nautilus, is regarded as ahead of its time, since it accurately describes many features of today's submarines, which in the 1860s were comparatively primitive vessels.