Mississippi Mermaid (French: La Sirène du Mississipi) is a 1969 romantic crime drama film written and directed by François Truffaut and starring Jean-Paul Belmondo and Catherine Deneuve. Adapted from the 1947 novel Waltz into Darkness by William Irish, the film follows a tobacco planter on the island of Réunion who becomes engaged through correspondence to a woman he does not know. When she arrives, it is not the same woman in the photo, but he marries her anyway.

Shot in Southern France and on Réunion, Mississippi Mermaid was the 16th highest-grossing film of 1969 in France, with a total of 1,227,657 admissions. It was remade in 2001 as Original Sin, directed by Michael Cristofer and starring Angelina Jolie and Antonio Banderas.