William Peter Blatty's novel sold poorly at first but shot to the top of the New York Times bestseller list after he discussed the existence of the devil on The Dick Cavett Show.

Blatty struggled to get the novel adapted before publication; a modest offer from Lew Grade fell through over Blatty's insistence on producing, and a co-production deal with Paul Monash collapsed when Blatty discovered Monash was trying to take control of the film.

Studios initially considered major stars for the leads, including Audrey Hepburn, Anne Bancroft and Jane Fonda for Chris, and Jack Nicholson or Paul Newman for Karras, before relatively unknown actors Ellen Burstyn, Jason Miller and Linda Blair were cast, against studio wishes.

Jason Miller was cast as Father Karras after Friedkin gave him the novel following a play performance; Miller, who had studied for the Jesuit priesthood and experienced a spiritual crisis similar to Karras's, told Friedkin 'He is me,' and the studio had to buy out already-signed actor Stacy Keach's contract.

Linda Blair was cast after showing up unannounced with her mother; during her interview she candidly described the film's masturbation scene and asked Friedkin if he had ever masturbated, convincing him of her natural, unprecocious personality.

Mercedes McCambridge voiced the demon Pazuzu, eating raw eggs, drinking whiskey, and chain-smoking to roughen her voice, but Warner Bros. initially left her uncredited until a Screen Actors Guild arbitration forced her inclusion in most prints.

Stuntwoman Eileen Dietz, 15 years older than Blair, performed many of the film's most violent or disturbing possession scenes as Blair's double and is the face seen as the demon in close-ups, though a dispute arose over how much screen time she actually had.

Filming took place in Iraq near Mosul at a time when the US and Iraq had no diplomatic relations, forcing Friedkin to negotiate directly with local Ba'ath Party officials, who required him to hire and train local crew; daytime temperatures reached 130°F, limiting shooting to dawn and dusk.

To achieve visible breath during the exorcism scenes, a $50,000 refrigeration system cooled the bedroom set to -20°F, but the set lighting warmed the air so quickly that filming was limited to three-minute bursts, and the whole scene took a month to shoot.

Friedkin manipulated actors for genuine reactions, including slapping Father William O'Malley before a take, firing blank gunshots without warning to startle Jason Miller, and secretly rehearsing the vomit effect to hit Miller's chest before redirecting it into his face during the actual take.

The production suffered numerous mishaps fueling belief in a curse: a fire caused by a bird flying into a circuit breaker destroyed most of the house sets, a 10-foot Pazuzu statue was mistakenly shipped to Hong Kong instead of Iraq, and several cast and crew members died or were injured during the shoot, including actors Jack MacGowran and Vasiliki Maliaros.

Ellen Burstyn suffered a permanent spinal injury after being thrown backward in a stunt used in the final film, and Linda Blair fractured her lower spine after being too loosely strapped to the rocking bed rig, developing lifelong scoliosis and a cold aversion from filming in the refrigerated set.

The famous head-spinning effect was achieved using a realistic life-size animated dummy of Regan built by makeup artist Dick Smith and effects supervisor Marcel Vercoutere, complete with a condom-based throat that could bulge and a tube for simulated breathing.

Makeup artist Dick Smith spent four hours each morning aging Max von Sydow by roughly 30 years for the role of Father Merrin, an effect so convincing that critic Pauline Kael called it one of the most convincing aging jobs she'd seen.

The iconic shot of Father Merrin arriving in fog beneath a streetlamp was inspired by René Magritte's painting Empire of Light and required removing the house's fake window frame to hide a spotlight between it and the real window; Friedkin was satisfied with the first take despite gusting wind threatening the fog effect.

The spider-walk stunt was performed by gymnast Ann Miles without the special harness designed for it, but Friedkin cut the scene before release; its existence was debated by fans for years until critic Mark Kermode found the footage in the Warner Bros. archive and it was restored for the 2000 director's cut.

Some audience members fainted or vomited during screenings, particularly during the realistic angiography scene, and the film's disturbing content led several cities to attempt bans or restrict children from attending despite its R rating.

The Exorcist became the first horror film nominated for the Academy Award for Best Picture, receiving ten nominations total, and won for Best Adapted Screenplay and Best Sound; it was the highest-grossing R-rated horror film until It surpassed it in 2017.