Warren Duff (May 17, 1904 – August 5, 1973) was a film and television writer and producer.As a writer, Duff wrote for films including, Fashions of 1934, Angels with Dirty Faces (1938), Experiment Perilous (1944), Step Lively (1944), Chicago Deadline (1949) and Appointment with Danger (1951).He worked on television programs including The Rogues (1965), The Invaders, (1967) and Mannix (1967).Duff, the producer of the film noir classic Out of the Past (1947), was once an actor and director on the New York City stage before turning to screenwriting when he entered the film business in 1931.