The origins of the film came from Reiner's return to single life after a divorce. Ephron interviewed Reiner and it provided the basis for Harry. Sally was based on Ephron and some of her friends. Crystal came on board and made his own contributions to the screenplay, making Harry funnier. Ephron supplied the structure of the film with much of the dialogue based on the real-life friendship between Reiner and Crystal. The soundtrack consists of standards performed by Harry Connick, Jr., with a big band and orchestra arranged by Marc Shaiman. Connick won his first Grammy for Best Jazz Male Vocal Performance.
Columbia Pictures released the film using the "platform" technique, which involved opening it in a few select cities letting positive word of mouth generate interest and then gradually expanding distribution over subsequent weeks. When Harry Met Sally... grossed a total of US$92 million in North America, well above its $16 million budget. Ephron received a British Academy Film Award, an Oscar nomination, and a Writers Guild of America Award nomination for her screenplay. The film is 23rd on AFI's 100 Years... 100 Laughs list of the top comedy films in American cinema and number 60 on Bravo's "100 Funniest Movies". In early 2004, the film was adapted for the stage in a production starring Luke Perry and Alyson Hannigan.
Throughout the film several diverse couples reflect on their relationship histories: how they met, courted, and married. These couples are not part of the plot, but the main characters tie into their stories.
In 1977, Harry Burns and Sally Albright finish college at the University of Chicago (in scenes shot on location at the University) and meet while carpooling to begin their careers in New York City. At the time, Harry is dating a friend of Sally's. The film examines their ideas about relationships between men and women. It is Harry's view that, "Men and women can't be friends because the sex part always gets in the way." Sally disagrees, claiming that men and women can be strictly friends without sex. This argument becomes an underlying theme to the movie. On the way, at a stop in a diner, Sally is angered when Harry tells her she is attractive; she accuses him of making a pass at her. In New York, due to their divergent philosophies, they depart less than friendly.
Five years later they meet in a New York airport, and find themselves on the same airplane. Both are in relationships; Sally has just started dating a man named Joe, and Harry is engaged to a woman named Helen, which surprises Sally. Harry suggests they become friends, forcing him to elaborate on his previous rule about male-female friendships; they can never be friends because sex will always be in their way spoiling it. They separate concluding that they will not be friends.
Harry and Sally meet again five years later in a New York bookstore. Their earlier relationships have ended, and they have coffee together where they talk about their previous relationships. After leaving the café, they take a walk and decide to become friends. In the scenes that follow, they have become very close friends having late night phone conversations, going to dinner, and spending a lot of time together. Their dating experiences with other people during this time highlights their different approaches to relationships and sex.
During a New Year's Eve party Harry and Sally find themselves attracted to each other. Though they remain friends, they set each other up with their respective best friends, Marie and Jess. The four go to a restaurant, where it is Marie and Jess that hit it off and end up getting married. Sally, however, breaks down crying once she hears the news that her ex, Joe, has gotten married. Harry, who has been listening to her crying over the phone, goes over to her apartment to comfort her. They have sex that night, resulting in an awkward moment next morning as Harry quickly leaves Sally's apartment. This creates tension in their relationship, as the two have a heated argument during Jess and Marie's wedding dinner that leads to their friendship cooling for three weeks. At a New Year's Eve party that year, Sally feels alone without Harry by her side. When she decides to leave the party early, Harry walks in and declares his love for her, and they make up and kiss. It is shown in the last segment of the movie that Harry and Sally have gotten married, and they are the last couple who discuss their relationship history.
She then proceeded to interview Reiner and Scheinman about their lives in order to have material on which to draw. These interviews also provided the basis for Harry. Reiner was constantly depressed, pessimistic yet very funny. Ephron also got bits of dialogue from these interviews. Sally was based on Ephron and some of her friends. She worked on several drafts over the years while Reiner made Stand By Me and The Princess Bride. Billy Crystal came on board when the project was called Boy Meets Girl and made his own contributions to the screenplay, making Harry funnier. The comedian "experienced vicariously" Reiner's (his best friend at the time) return to single life after divorcing comedienne/filmmaker Penny Marshall and in the process was unconsciously doing research for the role of Harry.
During the screenwriting process when Ephron would not feel like writing, she would interview people who worked for the production company. Some of the interviews appeared in the film as the interludes between certain scenes featuring couples talking about how they met, although the material was rewritten and reshot with real actors. Ephron supplied the structure of the film with much of the dialogue based on the real-life friendship between Reiner and Crystal. For example, in the scene where Sally and Harry appear on a split screen, talking on the telephone while watching their respective television sets, channel surfing, was something that Crystal and Reiner did every night.
Originally, Ephron wanted to call the film, How They Met and went through several different titles. Reiner even started a contest with the crew during principal photography - whoever came up with the title won a case a champagne. In order to get into the lonely mindset of Harry when he was divorced and single, Crystal stayed by himself in a separate room from the cast and crew while they were shooting in Manhattan. The script initially ended with Harry and Sally remaining friends and not pursuing a romantic relationship because she felt that was "the true ending", as did Reiner. Eventually, Ephron and Reiner realized that it would be a more appropriate ending for them to marry, though they admit that this is generally not a realistic outcome.
When posed the film's central question, can men and women just be friends, Ryan replied, "Yes, men and women can just be friends. I have a lot of platonic (male) friends, and sex doesn't get in the way." Crystal said, "I'm a little more optimistic than Harry. But I think it is difficult. Men basically act like stray dogs in front of a supermarket. I do have platonic (women) friends, but not best, best, best friends."
The film may be best known for a scene featuring the two title characters having lunch at Katz's Deli in Manhattan. They are arguing about a man's ability to recognize when a woman is faking an orgasm. Sally claims men cannot tell the difference, and to prove her point, she vividly (but fully clothed) demonstrates the skill as other diners watch. The scene ends with Sally casually returning to her meal as a nearby patron, played by Reiner's mother, places her order: "I'll have what she's having." This scene was shot again and again, and Ryan demonstrated her fake orgasms for hours and hours.
This classic scene was born when the film started to focus too much on Harry. Crystal remembers saying, "'We need something for Sally to talk about,' and Nora said, 'Well, faking orgasm is a great one,' and right away we said, 'Well, the subject is good,' and then Meg came on board and we talked with her about the nature of the idea and she said, 'Well, why don't I just fake one, just do one?'" Ephron suggested that the scene take place in a deli and it was Crystal who came up with the scene's classic punchline – "I'll have what she's having." In 2005, the quote was listed 33rd on the AFI's 100 Years... 100 Movie Quotes list of memorable movie lines. Reiner recalls that at a test screening, all of the women in the audience laughing while all of the men were silent.
Arrangements and orchestrations on "It Had to Be You", "Where or When", "I Could Write a Book", and "But Not for Me" are by Connick and Shaiman. Other songs were performed as piano/vocal solos, or with Connick's trio featuring Benjamin Jonah Wolfe on bass and Jeff "Tain" Watts on drums. Also appearing on the album are tenor saxophonist Frank Wess and guitarist Joy Berliner. The soundtrack went to #1 on the Billboard Traditional Jazz Chart and was within the top 50 on the Billboard 200. Connick also toured North America in support of this album. It went on to reach double-platinum status.
Rita Kempley's review in the Washington Post praised Meg Ryan as the "summer's Melanie Griffith – a honey-haired blonde who finally finds a showcase for her sheer exuberance. Neither naif nor vamp, she's a woman from a pen of a woman, not some Cinderella of a Working Girl. Mike Clark, of USA Today, gave the film three out of four stars, writing, "Crystal is funny enough to keep Ryan from all-out stealing the film. She, though, is smashing in an eye-opening performance, another tribute to Reiner's flair with actors. David Ansen provided one of the rare negative reviews of the film for Newsweek. He criticized the casting of Crystal, "Not surprisingly he handles the comedy superbly, but he's too cool and self-protective an actor to work as a romantic leading man", and felt that as a film, "of wonderful parts, it doesn't quite add up".
In June 2008, AFI revealed its "Ten top Ten"—the best ten films in ten "classic" American film genres—after polling over 1,500 people from the creative community. When Harry Met Sally was acknowledged as the sixth best film in the romantic comedy genre.
In early 2004, the film was adapted for the stage in a Theatre Royal Haymarket production starring Luke Perry and Alyson Hannigan. Molly Ringwald and Michael Landes later replaced Hannigan and Perry for the second cast.