Francis Ford Coppola's original choice to play gangster Hyman Roth was James Cagney. He begged Cagney to take the role, even visiting him at his home, but Cagney turned him down. Submitted by wizard_of_gore

Originally the character of Connie was supposed to be played by someone Coppola called " plain looking, the daughter of a big-shot who is only married off because she's the daughter of some big Mafioso guy". When they couldn't find an actress, Thalia, Coppola's sister, got the part, even though Coppola thought she was too beautiful and said "C'mon, look at her, who wouldn't want to marry her."

Al Pacino and Diane Keaton actually fell in love during the shoot, and were a couple for quite some time.

Although Coppola was advised not to talk to real Mafioso because they would never stop bugging him and it might change how he filmed the movie, James Caan did spend time with various Mafia heads, and got much of his character quirks, expressions and gestures from them.