William Kotzwinkle (born November 22, 1938; 87 years ago (November 22, 1938), or 1943; 83 years ago (1943) according to different sources) is an American novelist, children's writer, and screenwriter. He was born in Scranton, Pennsylvania, U.S.A. He won the World Fantasy Award for Best Novel for Doctor Rat in 1977, and has also won the National Magazine Award for fiction. Kotzwinkle is known for writing the novelization of the screenplay for E.T. the Extra-Terrestrial.

He has been married to author Elizabeth Gundy since 1965.