8½ (1963) was shot, like almost all Italian movies at the time, completely without sound recording on set. All dialogue was dubbed during post production. Federico Fellini was known for shouting direction at his actors during shooting, and for rewriting dialogue afterwards, making a lot of the dialogue in the movie appear out-of-sync. (Source: High-def Digest)
Federico Fellini attached a note to himself below the camera's eyepiece which read, "Remember, this is a comedy."
The title refers to the number of movies Federico Fellini had directed up until that point - six features, two shorts (films #7 and #8) and a co-directed film with Alberto Lattuada, for a total of 8 1/2 films.
Often cited by Federico Fellini himself as one of his favorite films ever, even considering other directors' works.
During the rehearsal scene, it seems that the love theme from The Godfather (1972) can be heard on the piano. It is, in fact, from Fortunella (1958). Nino Rota recycled his music from the former film for The Godfather. When this came to light, his Oscar nomination for The Godfather was withdrawn.