Nausea (French: La Nausée) is a philosophical novel by the existentialist philosopher Jean-Paul Sartre, published in 1938. It is Sartre's first novel.

The novel takes place in 'Bouville' (homophone of Boue-ville, literally, 'Mud town') a town similar to Le Havre. It comprises the thoughts and subjective experiences—in a personal diary format—of Antoine Roquentin, a melancholy and socially isolated intellectual who is residing in Bouville ostensibly for the purpose of completing a biography on a historical figure. Roquentin's growing alienation and disillusionment coincide with an increasingly intense experience of revulsion, which he calls "the nausea", in which the people and things around him seem to lose all their familiar and recognizable qualities. Sartre's original title for the novel before publication was Melancholia.

The novel has been translated into English by Lloyd Alexander as The Diary of Antoine Roquentin and by Robert Baldick as Nausea.