Jon Olav Fosse (Norwegian: [ˈjʊ̀nː ˈfɔ̂sːə]; born 29 September 1959) is a Norwegian author, translator, and playwright. In 2023, he was awarded the Nobel Prize in Literature "for his innovative plays and prose which give voice to the unsayable."

Fosse's work spans over seventy novels, poems, children's books, essays, and theatre plays, which have been translated into over fifty languages. The most performed Norwegian playwright after Henrik Ibsen, Fosse is currently—with productions presented on over a thousand stages worldwide—one of the most performed contemporary playwrights globally. His minimalist and deeply introspective plays, with language often bordering on lyrical prose and poetry, have been noted to represent a modern continuation of the dramatic tradition established by Henrik Ibsen in the 19th century. Fosse's work has often been placed within the tradition of post-dramatic theatre, while several of his notable novels have been described as belonging to the style of post-modernist and avant-garde literature, due to their minimalism, lyricism and unorthodox use of syntax.

Fosse was born in 1959 in Haugesund, Norway, and grew up in Strandebarm. His family were Quakers and Pietists, which he credits with shaping his spiritual views. A serious accident at age seven brought him close to death; Fosse saw a shimmering light and experienced peace and beauty: "I think this experience fundamentally changed me," Fosse recalled, "and perhaps made me a writer. He started writing around the age of twelve. As a teenager, Fosse was interested in becoming a rock guitarist, and he began to dedicate more time to writing once he gave up his musical ambitions. He also played the fiddle, and much of his teenage writing practice involved creating his own lyrics for musical pieces. Growing up, he was influenced by communism and anarchism and has described himself as a "hippie".

Fosse enrolled at the University of Bergen and studied comparative literature during which time he began writing in Nynorsk. His debut novel, Raudt, svart (Red, Black), was published in 1983 and was influenced by the Nynorsk writer Tarjei Vesaas. The novel contrasted with the social realist fiction popular in Norway at the time and emphasised linguistic expression rather than plot. He published a second novel, Stengd gitar (Closed Guitar) in 1985 and a poetic cycle, Engel med vatn i augene (Angel with Water in Its Eyes) in 1986. He gained a master's degree in comparative literature in 1987, again from the University of Bergen, and published his third novel, Blod. Steinen er (Blood. The Stone Is). Following his separation from his wife in 1989, Fosse published a novel and his first collection of essays. In the early 1990s, he continued to publish novels and worked with his second wife, Grethe Fatima Syéd, on several translations.

Fosse's first play, Og aldri skal vi skiljast (And We'll Never Be Parted), was performed and published in 1994. Fosse has written novels, short stories, poetry, children's books, essays, and plays. His works have been translated into more than forty languages. Between working on his novels, Fosse works as a translator of other authors' works.

Fosse wrote the libretto for the opera Asle og Alida (2025), composed by Bent Sørensen.

Fosse writes in Nynorsk. His plays are seen as a modern continuation of the tradition established by Henrik Ibsen in the 19th century. His prose works are often said to be closer to poetry than the traditional novel. Fosse considers himself primarily a poet, regardless of the literary form he is using. Fosse's native Vestlandet is a frequently present inspiration in his writing.

Fosse mentions Samuel Beckett, as well as Georg Trakl and Thomas Bernhard as his elective relatives. Other authors and books that have influenced his life and work include Olav H. Hauge, Knut Hamsun, Tarjei Vesaas, Franz Kafka, William Faulkner, Virginia Woolf, and the Bible.