The 31st Cannes Film Festival was held from 16 to 30 May 1978. The Palme d'Or went to The Tree of Wooden Clogs by Ermanno Olmi. This festival saw the introduction of a new non-competitive section, 'Un Certain Regard', which replaces 'Les Yeux Fertiles' (1975-1977), 'L'Air du temps' and 'Le Passé composé'.

Bye Bye Monkey is a 1978 Italian-French comedy-drama film, directed by Marco Ferreri and starring Gérard Depardieu, Marcello Mastroianni, James Coco, Gail Lawrence and Geraldine Fitzgerald. It is about a man who finds a baby chimpanzee in a giant King Kong prop and decides to raise it like a son. It was filmed in English and shot in Long Island, New York. As this was a French-Italian co-production, French and Italian dubbed versions were made for their respective countries' theatrical releases.