Women have babies all the time. It's one of the things they're pretty well-known for. So why is Rosemary's Baby significant? Let's put on our smelly occult necklaces and investigate.
Roman Polanski earned an Oscar nomination for adaptation of Ira Levin's novel, and Ruth Gordon won the Oscar for best supporting actress as Mia Farrow's eccentric old neighbor. Farrow herself was nominated for a BAFTA (the British Academy Awards), a Golden Globe, and several other awards. The American Film Institute's 2001 list of the best "heart-pounding" movies had Rosemary's Baby at No. 9, between The French Connection and Raiders of the Lost Ark. (It's a weird list.)
The context: Rosemary's Baby had not even been published yet when uber-producer Robert Evans, head of production at Paramount Pictures, was shown a copy and urged to buy it. The man doing the urging was William Castle, the legendary B-movie director best known for gimmicks like installing vibrating motors under theater seats for The Tingler. Castle wanted to direct Rosemary's Baby, but Evans thought the book deserved, shall we say, a more sophisticated treatment than the man behind House on Haunted Hill and 13 Ghosts was liable to give it. Castle agreed to serve as producer, and he has a silent cameo as the silver-haired man waiting to use the phone booth after Mia Farrow.
Meanwhile, Polish director Roman Polanski was gaining attention for the movies he was making in Europe, including Knife in the Water (1962), Repulsion (1965) and Cul-de-sac (1966). Robert Evans, a fan of Polanski's, sent him Rosemary's Baby in the hopes that he'd make it his first American film, even though it would also be the first time he'd made a film from someone else's story. Polanski was hooked. He wrote the screenplay adaptation himself.
Rosemary's Baby became a huge bestseller after its March 1967 release, moving some 2.3 million copies by the time the movie opened 15 months later. Evans and Paramount wanted a "name" actress in the lead. They hired Mia Farrow, who had become famous through her work on the popular TV series Peyton Place and her out-of-nowhere marriage to Frank Sinatra in 1966, when she was 21 and he was 50. (He served her with divorce papers while Rosemary's Baby was being shot.) Robert Redford turned down the male lead, and John Cassavetes, an actor who would later make his mark as a director of independent films, took it instead.
Levin's novel was partly inspired by Anton LaVey's Church of Satan, a group founded in 1966 that had garnered ample publicity in the news media. These were tumultuous times in American culture, and religiosity in general was declining as more and more people questioned their beliefs and turned to new ones. The April 8, 1966, issue of Time magazine -- which Rosemary is seen reading in the movie -- asked: "Is God Dead?" It was the right time for a story about the fundamental battle between Good and Evil, and how such a battle might play out in modern life.
Rosemary (Mia Farrow) and Guy (John Cassavetes) are a newly married couple who move into a charming old apartment in a building next to Central Park. (In real life, it's the Dakota building, later infamous as the site of John Lennon's murder.) Their neighbors are an odd elderly couple, the Castevets (Ruth Gordon and Sidney Blackmer). Rosemary gets pregnant, but something seems wrong from the very beginning.
What it influenced: Rosemary's Baby was a financial success, ranking 5th at the box office among 1968 releases, and generally well received by critics. With this success came the usual benefits. Mia Farrow, an untested commodity on the big screen, was established as a credible movie star. Ruth Gordon, already a 50-year veteran of stage and screen, became buzzworthy when she won the Oscar, and that led to her being cast in another soon-to-be-classic, Harold and Maude (1971).
As for Roman Polanski, he was now the European director who'd hit a home run his first time at bat in Hollywood. But there were tragic and unforeseeable consequences as well. A year after Rosemary's Baby was released, his wife, Sharon Tate, and four others were killed by Charles Manson's insane followers at the Polanskis' L.A. home. (Polanski was in London on business.) Tate was 8 1/2 months pregnant at the time. Not only did this give the tragedy an eerie similarity to Rosemary's Baby, but it wouldn't have happened at all if Polanski hadn't made the film, moved to Los Angeles, and become part of the Hollywood scene. Of course, without all that he wouldn't have met Tate in the first place. So it goes.
Rosemary's Baby kicked off a fun new trend in movies: Satan! He'd been referenced in movies before, of course, but now his popularity surged with a new cycle of films about black magic, devil worship, and the like. Some of these were nothing more than low-budget B-movies capitalizing on a trend (e.g., The Brotherhood of Satan, 1971), while others, like The Exorcist (1973) and The Omen (1976) were more serious.
What to look for: Roman Polanski has said that when he read the novel, the first several pages made him think it was a soap opera. There is nothing chilling about the movie's early scenes -- nor, indeed, about most of the scenes that follow. This is not a movie full of scares or terror. Instead, it creates a slow-building sense of dread and doom, playing on that most instinctive of fears: a woman's concern for her unborn child.
The film discusses the mechanics of pregnancy rather frankly, with Rosemary mentioning her period and coordinating with Guy on when she'll be most likely to conceive. When things go awry with the pregnancy, she even says flat-out that she's not going to have "an abortion" -- one of the very few times that the word had been uttered in an American film.
What's the Big Deal?
Rosemary's Baby started a new cycle of movies about the occult and Satanism, and scared audiences without any gore or major violence. It also established Roman Polanski as an important Hollywood director, which led to Chinatown, followed by Polanski's rape scandal and subsequent flight to Europe, where he remains to this day.
Further reading: These contemporary reviews, more than usual, cheerfully divulge every single element of the film's story. So don't read them until after you've seen the movie: Roger Ebert, The New York Times, Time magazine.
For a thorough analysis of the movie's symbolism and themes, read Tim Dirks' excellent (and detailed) essay -- but, again, only after you've watched the movie.
Related columns: What's the Big Deal?: Chinatown (1974).