- The title role was originally intended for Frank Sinatra, but he injured his hand in an accident, and the role was then offered to John Wayne, Steve McQueen and Paul Newman, finally being accepted by Clint Eastwood.
- American war hero and actor Audie Murphy was first approached to play the villian. Murphy was killed in a plane crash in 1971 and it is not known whether he had said he would or would not take the part.
- After Harry has foiled the bank robbery at the beginning of the film, he strides over to the one surviving robber. In doing so, he walks in front of a theater which is showing Play Misty for Me (1971), which Eastwood directed and starred in.
- Opening sniper scenes shot from atop San Francisco's Bank of American Building on California Street. The sniper's target is a girl swimming in the pool on the roof of the Holiday Inn in Chinatown a few blocks north on Kearny Street.
- When Callahan is being run all over town by Scorpio, he passes a wall which bears the graffiti "Kyle", the name of Eastwood's son.
- The final scene where Harry throws his badge in the river is a homage to a similar scene from High Noon (1952).
- Andrew Robinson (Scorpio) had to get an unlisted phone number, and has received a death threat. Robinson, who turned his character into one of the screen's great psycho killers, was in real life a committed pacifist, and was so terrified of guns that every time he had to fire one in the film, he would squeeze his eyes shut and flinch violently. Director Don Siegel had to shut down production for almost a week and hire a firearms expert to work with Robinson continiously until he was realistically able to fire a gun.
- It is widely accepted that the movie was loosely based on the events surrounding the Zodiac Killer who was actively killing people in San Francisco at the time.
- Reni Santoni who plays Harry's partner Chico Gonzales, later once again played a partner to another crook-shooting rogue policeman, in Cobra (1986). And, once again, that character's name was Gonzales.
- When director Don Siegel fell ill during the shoot, Eastwood took over the helm and directed two scenes: Harry's late night rescue of a would-be suicide jumper and Harry's homosexual encounter in San Francisco's Mt. Davidson Park.
- Eastwood performed all of his own stunts, the most dangerous of which, was the jump from the bridge onto the roof of a moving hijacked school bus.
- In an earlier version of the script, when the fallen bank robber calls Harry's bluff as to the "six shots of only five" question, Harry puts the gun to his own head.
- Followed by four sequels: Magnum Force (1973), The Enforcer (1976), Sudden Impact (1983) and The Dead Pool (1988).
WRITERS: Harry Julian Fink, Rita M. Fink, Dean Riesner and John Milius (uncredited).
PRODUCER: Don Siegel.
ASSOCIATE PRODUCER: Carl Pingitore.
EXECUTIVE PRODUCER: Robert Daley.
ORIGINAL MUSIC: Lalo Schifrin.
DISTRIBUTOR: Warner Bros.
Harry: Have what?
The Mayor: A report! What have you been doing?
Harry: Well, for the past three quarters of an hour, I've been sitting on my ass in your outer office waiting on you!
Rothko: How do you know?
Harry: 'Cause he likes it.
Gonzales: How does he feel about Mexicans?
De Georgio: Ask him.
Harry: Especially Spics.
The Mayor: Intent? How did you establish that?
Harry: When a man is chasing a woman through an elley with a butcher's knife and a hard-on, I figure he isn't out collecting for the Red Cross!
Harry: Yeah, I've been following him on my own time. And anybody can tell I didn't do that to him.
Chief: How?
Harry: Cause he looks to damn good, that's how.