Peter O'Toole was originally cast as Toby Dammit. After he pulled out, Federico Fellini contacted a London casting agency and asked them to send the most decadent actors they had to Rome to see him. They sent Terence Stamp and James Fox, and Fellini chose Stamp.
While filming the "Metzengerstein" segment with his sister Jane Fonda and brother-in-law Roger Vadim in Roscoff, Brittany, Peter Fonda would spend up to 4 hours a day working on the script that would become Easy Rider (1969). Terry Southern, who had worked on Barbarella (1968) with Vadim, visited the set and would help Fonda with his script, getting a co-writer credit on "Easy Rider" in the process.
Louis Malle had originally wanted then-model Florinda Bolkan to play the part that eventually went to Brigitte Bardot.
In Federico Fellini's segment, Terence Stamp plays an actor arriving in Rome to do a film, and as they leave the airport to go into the city he suddenly sits up and asks where his Ferrari is; he was promised a Ferrari. This is a humorous reference to a behind the scenes situation on the film Hexen von heute (1967) from the year before, when Clint Eastwood was enticed to play a small role in exchange for a Ferrari.