The orange Volkswagen Beetle that Steve McQueen and Ali MacGraw pass as they flee town after the bank heist is driven by James Garner. Garner had been visiting a friend on the shoot and was hired for his vehicular skills by stunt coordinator Carey Loftin.
Writer Jim Thompson was originally hired to adapt his own novel for the movie. Thompson worked on the screenplay for four months and produced a prose treatment, a first draft, and alternate scenes and episodes. Thompson's script included the original borderline-surrealistic ending of the novel featuring the kingdom of El Rey. Steve McQueen objected to the depressing ending and had Thompson replaced with rising screenwriter Walter Hill.
Actual marked police cars were used for two of the towns used for shooting. You can see "San Marcos Police Department" on two cars in the chases and crashes after the bank job, and "Sierra Blanca Police" on a car chasing Doc and Carol from the drive-in restaurant near El Paso.
In the scene where Steve McQueen and Ali MacGraw are standing outside the car and McQueen suddenly slaps her, the slap was unscripted, as can be seen by McGraw's shocked reaction.
The film was rated PG by the MPAA in the United States. A few years later, in retrospect, this was considered a mistake and the board believed that the film should have been rated (what was then) one step higher, an R.
The film's original score was composed by frequent Sam Peckinpah collaborator Jerry Fielding, but was replaced, at Steve McQueen's insistence, with the lighter, jazzier film score by Quincy Jones, shortly before the film's release.
W. Dee Kutach, the Texas prison parole board chairman who denies Doc McCoy (Steve McQueen) his parole in the opening minutes of the film, was actually a prison official at the time the movie was made - he was the Assistant Director for Treatment for the Texas Department of Corrections in Huntsville, TX.
The movie was supposed be directed by Peter Bogdanovich and star Cybill Shepherd, his girlfriend at the time. When Shepherd was replaced by Ali MacGraw. Bogdanovich left the project and was replaced with Sam Peckinpah. MacGraw then fell in love with costar Steve McQueen and broke up with her husband, Paramount production executive Robert Evans.
When Carol McCoy lists the exits to the First Bank of Beacon City, "One on Hopkins, one at Guadalupe Street, and one is the alley," she is listing the real-life exits of the actual shooting location in San Marcos, Texas.
Evocative harmonica solos courtesy of jazz great Toots Thielemans. The music played at the end titles quite obviously quotes Thielemans' best-known composition "Bluesette".