Actor Sidney Poitier gave up his usual salary and agreed to do the film for a smaller amount and a percentage of the profits. He won the Best Actor Oscar for his efforts.
Director Ralph Nelson had to put up his house as collateral.
Filmed on location in the City of Tucson. The church doors were borrowed from the Chapel in Sasabe, Arizona.
Shot on location in Arizona in only 14 days.
Since the story's action was tied to the chapel's construction, crew had to work through the night to keep up with it "progress" in the film. The actual building was real and could have stood for decades, but because it was built on rented property, it had to be demolished immediately after the filming was completed.
The title comes from the Sermon on the Mount.
When singing, the nuns were thought to have been too good. They were told to sing worse and sang horribly. The scene was dubbed over after the voices were flattened in editing.