Shot in black and white so that the characters wouldn't be upstaged by the romantic setting of Rome.
The airplane in which the Secret Service men arrive to search for Princess Ann is a very unusual type, the Breda-Zappata BZ.308, of which only one prototype was built in 1949 (for the Italian Air Force). It was scrapped shortly after its appearance in the movie.
The Embassy Ball sequence featured real Italian nobility, who all donated their salaries to charity. The reporters at the end of the film were real, too.
The first American film to be made in its entirety in Italy.
The leads' tandem use of the Italian Vespa 2-stroke scooter kindled an unprecedented public interest in the vehicle after the movie's release.
The original writer, Dalton Trumbo, was blacklisted as one of the legendary Hollywood Ten, and therefore could not receive credit for the screenplay, even when it won the Academy Award for Best Screenplay. Instead, his friend, Ian McLellan Hunter, took credit for the story and accepted the Oscar. Trumbo's wife, Cleo, was finally presented with the award in 1993, long after his death in 1976. The Oscar she received was actually a second one, because Hunter's son wouldn't give up his father's Oscar. Thus, two awards for Best Screenplay of 1953 exist. The story credit was corrected to credit Trumbo when the restored edition was released in 2002, nearly fifty years after the original release.
The Roman summer was stiflingly hot, with the temperatures in the high 90s. Crowds swarmed over all the locations, making huge impromptu audiences for the actors. Meanwhile, Italy itself was beset with clashes between political parties that resulted in strikes and unrest that threatened to disrupt production.
The sheet of paper Hennessy (Hartley Power) reads the interview questions from is actually a page of the script.
The story was originally optioned by Frank Capra in 1949, who had hoped to cast Cary Grant and Elizabeth Taylor in what would essentially amount to being a variation on his Oscar-winning classic, It Happened One Night. However, Capra's Liberty Films production company was beset with financial problems and he was forced to sell the property to Paramount where a combination of political timidity (Capra discovered the involvement of blacklisted writer Dalton Trumbo) and a tight budget prompted him to withdraw from the project. William Wyler, however, had no compunctions whatsoever about working with Trumbo.
When Gregory Peck came to Italy to shoot the movie, he was privately depressed about his recent separation and imminent divorce from his first wife, Greta Kukkonen. However, during the shot he met and fell in love with a French woman named Veronique Passani. After his divorce, he married Passani and they remained together for the rest of his life.
When filming the scene where the princess (Audrey Hepburn) says her goodbyes to Joe, the inexperienced Hepburn was unable to produce the necessary tears, eventually causing director William Wyler to complain at the number of wasted takes. Hepburn promptly burst into tears and the scene was filmed successfully.
With a budget of about $1.5 million, the film took $5 million in the domestic market.