According to Dario Argento, who is credited with co-writing the film's original story, he and Bernardo Bertolucci were on the set during the filming, and both constantly rewrote the script.
Co-produced by Safran and San Marco.
Color by Technicolor; shot in TechniScope on location in Monument Valley, also Spain and Cinecitta Studio in Rome, Italy.
The film has been shown on the AMC Cable Network in Letterbox format, in its original uncut version.
When Henry Fonda first received the script from Leone, he was not impressed with it. But close friend Eli Wallach, who had been in Leone's "The Good, the Bad, and the Ugly," convinced him to take the part. Wallach told Fonda that Leone used the script only as an outline for the film, which was improvised as the production went on and strengthened by the addition of evocative music and stylized action. Fonda got hold of the scripts of other Leone films, and then watched the finished products; he quickly realized that what Wallach had told him was true.
Original distributor United Artists refused to release the film with Henry Fonda cast as the cold-hearted, sadistic killer in the lead role, so Leone took the deal to Paramount, who ultimately distributed the film.
The music, composed by Ennio Morricone, is broken up into the following themes and sections:
1. Once Upon a Time in the West
2. As a Judgment
3. Farewell to Cheyenne
4. The Transgression
5. The First Tavern
6. The Second Tavern
7. Man with a Harmonica
8. A Dimly Lit Room
9. Bad Orchestra
10. The Man
11. Jill's America
12. Death's Rattle
Music published by Famous Music. Corp (ASCAP), distributed by BMG Music.