The movie was originally intended to be shot in Czechoslovakia, but the Russian invasion of that country in 1968 forced a change in plans.
Other titles considered for this film were "Two By Two", and "Louis, There's A Crowd Downstairs!"
Gene Wilder wanted Charles Grodin to play the part of Charles/Pierre, but Grodin declined, having committed to directing the original Broadway production of Lovers and Other Strangers.
Orson Welles did his narration in two days. It should be noted, however, that the narration which occurs in the middle section of the film, when Welles is not actually on-camera, is spoken by a quite different voice.