Dan Aykroyd originally conceived Ghostbusters as a project starring himself and John Belushi traveling through time and space battling supernatural threats, but the concept was deemed financially impractical after Belushi's death in 1982.

Aykroyd's fascination with the paranormal came from his family: his father wrote a book on ghosts, his mother claimed to see ghosts, his grandfather experimented with radios to contact the dead, and his great-grandfather was a renowned spiritualist.

Because the title 'Ghostbusters' was legally tied to a 1970s children's show owned by Universal, alternative titles like 'Ghoststoppers,' 'Ghostbreakers,' and 'Ghostsmashers' were considered until Columbia bought the rights for $500,000 plus 1% of profits.

Bill Murray joined the project without an explicit agreement, which was how he often worked, after Aykroyd turned to him following Belushi's death.

Michael Keaton, Chevy Chase, Tom Hanks, Robin Williams, Steve Guttenberg, and Richard Pryor were all considered for the role of Peter Venkman before it went to Bill Murray.

Ernie Hudson auditioned five times for the role of Winston Zeddemore, and the night before shooting began he received a new script drastically reducing his role so Bill Murray's part could be expanded.

Sigourney Weaver won over the filmmakers during her audition by walking on all fours and howling like a dog, despite initial resistance due to her serious roles in Alien and The Year of Living Dangerously; it was also her idea for Dana to become possessed by Zuul.

John Candy was offered the role of Louis Tully but turned it down after suggesting the character have a German accent and multiple German Shepherds, an idea the filmmakers rejected since there were already enough dogs in the film.

The role of Gozer was originally intended for Paul Reubens; when he passed, Yugoslavian actress Slavitza Jovan was cast and the character was redesigned with an androgynous look inspired by Grace Jones and David Bowie, with her dialogue dubbed by Paddi Edwards due to Jovan's strong accent.

During filming at 55 Central Park West, city officials closed adjacent streets during rush hour, causing traffic to back up all the way to Brooklyn, and when angry citizens asked what was being filmed, producer Joe Medjuck blamed it on Francis Ford Coppola's The Cotton Club.

Science-fiction writer Isaac Asimov personally complained to Aykroyd about the film's shoot inconveniencing his building during production.

Filming in the New York Public Library's main reading room was only permitted in the early morning and had to conclude by 10:00 am.

Special effects artist Steve Johnson took at least three grams of cocaine and completed the final design for the Slimer ghost puppet in one night after struggling with executive interference.

There were eighteen foam Marshmallow Man suits costing $25,000-$30,000 each, and seventeen of them were burned during filming; the actor wearing the suit needed a separate air supply due to the foam's toxicity.

The 'marshmallow' raining down on the crowd was actually shaving cream; after William Atherton insisted the intended 150 pounds be tested first and it knocked a stuntman down, the crew used only 75 pounds, which still gave some cast members skin rashes after hours of filming.

The Ectomobile's siren sound was created by sound designer Richard Beggs from a recording of a leopard snarl, cut and played backward.

Approximately 50 to 60 different theme songs were developed by various artists before Ray Parker Jr.'s 'Ghostbusters' was chosen; Huey Lewis was originally approached but was already committed to Back to the Future.

Composer Elmer Bernstein used the ondes Martenot, an instrument similar to a theremin, to create the film's eerie effects, and had to bring in a musician from England since there were so few trained ondists.

Ghostbusters was the number-one film in US theaters for seven consecutive weeks and became the highest-grossing comedy film ever at the time of its release.

At an early test screening for industry members, executives reacted poorly; one told Bill Murray and Dan Aykroyd's agent 'Don't worry: we all make mistakes,' while Coca-Cola's chairman said 'Gee, we're going to lose our shirts.'