Development
In the early 1990s, following the release of Ghostbusters II, Dan Aykroyd wrote a script for a third Ghostbusters film tentatively titled Ghostbusters III: Hellbent. In the script, the Ghostbusters are transported to a parallel-universe version of Manhattan called Manhellton, where the people and places are "hellish" versions of Earth, and the characters meet and confront the Devil. At the time, Aykroyd stated that Columbia Pictures was interested, though the principal actors, especially Bill Murray, were not. The Hellbent script's main characters are a new, younger group of Ghostbusters; Ray, Egon and Winston struggle to keep the business going after Peter's relationship with Dana becomes serious. Elements of this story were used in Ghostbusters: The Video Game (2009), which Aykroyd considered to be "essentially the third movie". At various stages of its development, Chris Farley, Chris Rock and Ben Stiller were reported as potential stars of a new Ghostbusters film.
By 2004, Columbia had begun pursuing a sequel but Murray, who disliked sequels, was uninterested in the project. The following year, Harold Ramis confirmed plans to introduce Stiller into the principal cast. By 2009, the project had failed to progress, but by January 2010, Ivan Reitman, director of the first two Ghostbusters films, confirmed he would direct a third one. Also in March, Murray discussed development of the film and his mixed feelings about reprising his role. A release was scheduled for Christmas 2012. That October, Aykroyd commented on the screenplay written by Gene Stupnitsky and Lee Eisenberg, stating that he was particularly impressed with the writing of Murray's character and the implementation of the new team with the original while he and Ramis worked on a second draft of the script.
By August 2011, Aykroyd stated that filming was scheduled to begin later that year with a story focused on passing the Ghostbusters mantle to the younger actors. When Murray decided against reprising his role, Aykroyd said another actor might replace him. Aykroyd also said he wanted retired actor Rick Moranis to return as Louis Tully. By February 2012, the film was placed on hold as the production team re-evaluated the project. Without Murray, the studio searched for replacement actors and considered including his character as a CGI-rendered ghost. In June, Murray again acknowledged all involved were attempting to develop the third film before dropping out of the film the following month. In July, Aykroyd confirmed the film was back in development with a script re-write from Etan Cohen. Aykroyd said of the script: "It's got to be perfect. That's the whole thing. There's no point in doing it unless it's perfect. So that's what we're up to now." By September, Reitman announced the developments of a remake. In May 2013, Aykroyd discussed plot points including real experiments being done by college students at Columbia University as a source of inspiration. The plot would revolve around research being done by the university, which would bring about threats from other dimensions. A new team of Ghostbusters would form to save Earth's plane of existence from supernatural threats. The script reportedly included Murray's character with hopes Murray would decide to join the production.
Following the death of Ramis on February 24, 2014, Sony/Columbia stated that Ramis would appear in a cameo appearance in the film. The film was delayed again to rework the script. By March 2015, Reitman was no longer attached to direct the third film, but would remain as producer, with plans to begin principal photography by early 2015. Weaver wanted her character's son to feature as a member of the team, and Reitman said he had already been included in the script.
A new film connected to the original two films was revealed in January 2019. Ivan Reitman's son Jason was confirmed to direct from a script he co-wrote with Gil Kenan while Ivan would serve as a producer. The film would feature teenagers—two males and two females—as the recruits for the Ghostbusters team.
Jason Reitman said the film ignores the events of 2016's Ghostbusters reboot, which was directed by Paul Feig. Reitman said he did not mean to snub the 2016 film and that he had "nothing but admiration" for Feig. Feig said Reitman had been a supporter of his film and that he "can't wait to see his take on the Ghostbusters universe". Reitman later said the idea of a teenage girl wanting to be a Ghostbuster had come to him, and with a positive reaction from Feig's film, proved the idea that anyone could be a Ghostbuster would work. Reitman also said the Ghostbusters franchise could readily expand on this idea with all types of people becoming Ghostbusters, personally thanking Feig for making this possible. Reitman considered, unlike the three prior Ghostbusters films—all of which involve people going into the ghostbusting business—he wanted to make this film about family first. With Kenan, Reitman created a script based around the Spengler family and the reason they are so disconnected. According to Dan Aykroyd, "Jason Reitman wrote a beautiful, heartfelt script that takes the real DNA from the first two movies and transfers that directly to the third, the next generation. It hands the legacy off to a new generation of stars, players, actors, and characters." Murray, who was also confirmed to be reprising Peter Venkman, was positive about the script. Ramis's daughter Violet (whom Reitman befriended during the filming of the first film), gave her blessing after reading an early version of the screenplay, saying that the story "captures the spirit of what the old movies are". She occasionally visited the sets and was (at the insistence of Reitman and propmaster Guillaume DeLouche) photographed wearing her late father's proton pack prop from the first film while prop makers from The Hand Prop Room in Los Angeles were building lighter replicas of it for Mckenna Grace to wear.
With a script centered around family, Reitman felt it was appropriate to change the backdrop from New York City to the American West to give the film a new identity and a different color palette. The script was structured to slowly reveal the connection to the Egon Spengler character, which would bring in elements of earlier Ghostbusters films. For example, the film sees Aykroyd's character return to running Ray's Occult Books, as seen in Ghostbusters II, but only the events of the original film are directly referenced.
