William Friedkin's "The Exorcist" has been exhaustively written about and studied since its December 26, 1973, theatrical release. Nothing quite like it had been seen before—there were reported faintings and even a miscarriage at screenings due to its oppressively disturbing subject matter—the film's mature meditation on the unknown and the nature of evil depicted with an uncompromising forthrightness. Adapted by William Peter Blatty from his 1971 novel, itself reportedly inspired by a real-life 1949 case of possession in Cottage City, Maryland, the handsome production went on to receive rapturous acclaim and ten Academy Award nominations. When lists of the all-time best horror movies are made, this title is frequently near, or all the way at the top, of the ranking. Virtually no one who has seen "The Exorcist" can forget where they were and the emotions it provoked upon first viewing. Whether a person has seen the film once or twenty times, however, the experience falters neither in significance nor cathartic potency.

During an archaeological dig in Northern Iraq, Father Merrin (Max von Sydow) stumbles upon an ancient amulet with the uncanny likeness of Pazuzu, a demon he once wrestled years before. His sinking belief that the succubus has returned coincides with unexplained sounds heard in the Georgetown home where actress Chris McNeil (Ellen Burstyn) is staying with 12-year-old daughter Regan (Linda Blair) as she shoots a movie in D.C. Chris thinks there might be rats in the attic, but her concern shifts to Regan's well-being when the young girl's mood and personality start to change soon after she begins playing with a Ouija board. Medical tests and a brain scan detect nothing out of the ordinary, but it soon becomes very apparent that Regan's body has been taken over by a diabolical entity. When Chris' director and new boyfriend Burke Dennings (Jack MacGowran) mysteriously falls to his death, the distressed mother must confront the reality that Regan, who was the only one home at the time of the incident, may have been responsible. Father Merrin and Damian Karras (Jason Miller), the latter a young priest currently facing a crisis of faith after the death of his elderly mother, are called in to investigate and eventually form the opinion that a Catholic exorcism might be necessary. What all involved witness will compel them to rethink everything they thought they knew about God and the sometimes nefarious forces existing beyond life and death.

"The Exorcist" carries with it either a stigma or a blessing. Frequently regarded as the scariest movie ever made, the film has nonetheless been extensively spoofed in comedies such as 1990's "Repossessed" (which starred Linda Blair alongside Leslie Nielsen) and 2001's "Scary Movie 2." Much of the profane dialogue that so shocked audiences decades ago has now entered the pop-culture lexicon, as have scenes involving head-spinning and projectile pea soup. This, alas, is the price that films as popular and passionately regarded as this one must sometimes pay. Fortunately, viewed on its own terms, "The Exorcist" has lost precious little of its power to still rattle one's nerves. Those jaded by its lampooning in other movies and media might even be surprised how much it still gets to them. Director William Friedkin lends his filmmaking a level of welcome prestige and intellect while sneaking a slice into one's jugular at precisely the right times.

Ellen Burstyn was nominated for an Oscar for her sterling performance as the embattled Chris McNeil, surrendering to the demands of a role that requires her to fight tooth and nail for the survival of her imperiled daughter. Chris, an atheist, cannot believe it when she turns to a Catholic priest for help, her outlook on religion transforming without her knowing quite how to handle it. She doesn't find God, necessarily, but something far more sinister and equally as unexplainable. A young Linda Blair also received an Academy nod as Regan; though her deviously throaty vocals were dubbed by Mercedes McCambridge in the possession sequences, this was more a technical requirement than a slight against Blair. She is utterly bloodcurdling in her effectiveness in the film's later scenes, standing at staggeringly poignant contrast to the sweet, bubbly preteen she plays in the first act. The rest of the main cast are filled with interesting character actors, each one getting down to the gritty authenticity of their part: Max von Sydow, as Father Merrin; then-stage actor Jason Miller, in his outstanding screen debut as the doubting Father Damian Karras; Lee J. Cobb, as Lieutenant William Kinderman; Jack MacGowran, as the ill-fated Burke Dennings, and Kitty Winn, as Chris' assistant and friend, Sharon Spencer.

A study in faith as much as in possession, "The Exorcist" ponders existential questions far larger than the human figures who desperately want to make sense of all the things they do not—nay, cannot—understand. Friedkin approaches the film as if he were capturing real lives in progress as an unearthly energy imposes itself onto them, making its leaps into the fantastically vicious and vile all the more tremulously affecting. Director of photography Owen Roizman breathes a thickly foreboding texture and autumnal specificity to the Georgetown area of Washington, D.C., its exterior locations (including the infamous staircase outside the McNeils' residence) continuing to draw tourists and passersby to this day. Also crucial to the picture's notoriety: the use of Mike Oldfield's atmospheric "Tubular Bells," as in a lovely early scene where Chris walks home from her movie set, the October leaves dancing around her, and Hans Werner Henze's dazzling "Fantasia For Strings" placed over the end credits. With darkness comes the need for hope and the dawn of a new day, and it is this sentiment that the film pitch-perfectly concludes upon (the altered ending of the Director's Cut, released in 2000, is not nearly as strong, trading in a contemplative grace note for something more saccharine and obvious). Without a doubt, "The Exorcist" is a touchstone in horror, seemingly incapable of taking a wrong step. Watching with the lights off is strongly encouraged. Turning them back on immediately afterwards will be a necessity.