September Affair is a 1950 American romantic drama film directed by William Dieterle and starring Joan Fontaine, Joseph Cotten, and Jessica Tandy. It was produced by Hal B. Wallis.

William Dieterle was a German-born actor and film director who emigrated to the United States in 1930 to leave a worsening political situation. He worked in Hollywood primarily as a director for much of his career, becoming a United States citizen in 1937. He moved back to Germany in the late 1950s.