Twenty Thousand Leagues Under the Sea is a classic science fiction adventure novel by French writer Jules Verne.

The book was widely acclaimed on its release and remains so; it is regarded as one of the premier 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.

During the year 1866 ships of various nationalities sight a mysterious sea monster which it is later suggested might be a gigantic narwhal. The U.S. government assembles an expedition in New York City to find and destroy the monster. Professor Pierre Aronnax a French marine biologist and the story's narrator is in town at the time and receives a last-minute invitation to join the expedition; he accepts. Canadian whaler and master harpooner Ned Land and Aronnax's faithful manservant Conseil are also among the participants.