Robert Redford originally agreed to play Blue and backed out at the last minute. He was sued by Paramount and afterward refused Roman Polanski's offer to play Guy Woodhouse in Paramount's Rosemary's Baby (1968).
The solo guitar passages in the film soundtrack were performed by Laurindo Almeida under the guidance of Manos Hatzidakis.
This was the first high-budget Hollywood film to be photographed by Stanley Cortez in many years - his reputation had declined in Hollywood because he was such a slow worker, even though the results were invariably impressive. On this film, according to leading man Terence Stamp, Cortez was aware that it was a "make-or-break" assignment and was determined to produce outstanding cinematography. But, perversely, this made him slower than ever and it was several times suggested that he be replaced. However, he kept his job, and, when the film was released, the beautiful photography was the one thing about it to be universally praised.
Terence Stamp did many scenes for this film without speaking. It was later claimed that he had been unable to master the required American accent (something remarked by many critics) and that a great many of his lines had been cut as a result.
Costume designer Edith Head began work on this film before her contract with Paramount ended in the spring of 1967. It is debatable how much of her finished work still remains in the completed film. However, she maintained in her personal record of 1000+ films she worked on during her career that this was one of her films.