"Nightfall" is a 1941 science fiction short story by the American writer Isaac Asimov about the coming of darkness to the people of a planet ordinarily illuminated by sunlight at all times. It was adapted into a novel with Robert Silverberg in 1990. The short story has appeared in many anthologies and six collections of Asimov stories. In 1968, the Science Fiction Writers of America voted "Nightfall" the best science fiction short story written prior to the 1965 establishment of the Nebula Awards and included it in The Science Fiction Hall of Fame Volume One, 1929–1964.

Isaac Asimov was an American writer and professor of biochemistry at Boston University. During his lifetime, Asimov was considered one of the "Big Three" science fiction writers, along with Robert A. Heinlein and Arthur C. Clarke. A prolific writer, he wrote or edited more than 500 books. He also wrote an estimated 90,000 letters and postcards. Best known for his hard science fiction, Asimov also wrote mysteries and fantasy, as well as popular science and other non-fiction.