The Unfaithful is a 1947 American murder mystery film noir directed by Vincent Sherman and starring Ann Sheridan, Lew Ayres and Zachary Scott. It was produced and distributed by Warner Brothers. Regarded by some as a film noir, the picture is based on the W. Somerset Maugham-penned 1927 play and William Wyler-directed 1940 film The Letter, which was reworked and turned into an original screenplay by writers David Goodis and James Gunn who shifted the setting from Malaya to the United States.

Lewis Frederick Ayres III was an American actor whose film and television career spanned 65 years. He is best known for starring as German soldier Paul Bäumer in the film All Quiet on the Western Front (1930) and for playing Dr. Kildare in nine films. He was nominated for an Academy Award for Best Actor for his performance in Johnny Belinda (1948).