Jean-Paul Sartre's philosophical novel La Nausée (1938; Nausea) is a seminal text of the existential movement that emerged in France during the 1940s and 1950s. In Nausea, Sartre, who became a figurehead of existential philosophy, explores fundamental questions and ideas that he elaborated upon in his later works.

Nausea is written as the diary of Antoine Roquentin, a thirty-year-old man who is grappling with a sense of revulsion at his consciousness of his own existence and of the existence of the people and objects around him. Roquentin, who is profoundly lonely, without friends or family, expresses a sensation of "sweetish sickness" in contemplating the absurdity of life. He refers to this sensation, which is both mental and physical, as the Nausea.

Nausea takes place primarily in the fictional French seaport town of Bouville, where Roquentin has been living for the past three years, while he works on research for a biography he is writing of an eighteenth-century French politician. Roquentin eventually decides to abandon the biography, as he has come to the conclusion that it is a meaningless project. He begins to hope that he and his former girlfriend, Anny, will get back together again and that their love will cure him of his Nausea. However, when he goes to visit Anny, she once again rejects him, and Roquentin is plunged into crisis, for his existence seems all the more repulsive to him. He ultimately resolves his philosophical crisis by deciding to take on the creative project of writing a novel, which he feels will be an antidote to the Nausea.

Nausea exemplifies a philosophical exploration of the nature of existence and the challenge faced by an individual who becomes keenly conscious of the fundamental absurdity of life. Sartre further explores themes of consciousness, loneliness, transformation, and freedom, in terms of his existential philosophy.