(at around 16 mins) James Wan was unavailable to return as director for the third installment due to his scheduling conflict with Furious 7 (2015). He makes a brief cameo as the theater director during Quinn's audition scene.

This third installment makes several references to ghosts and demons from the first two films of the "Insidious" franchise, such as the Lipstick Face Demon, The Bride in Black, and possibly the Long-Haired Fiend.

A trailer for the film was released in March of 2015 and featured the song "Afraid of Nothing" by Sharon Van Etten. The filmmakers used the song without acquiring the rights to it. When Van Etten was notified by a fan on Twitter, the filmmakers were forced to pay her for illegally using her music.

This film takes place in 2007. Insidious (2010) and Insidious: Chapter 2 (2013) take place in 2010.

Elise has a dog called Warren. It is based on real-life paranormal investigators Ed Warren and Lorraine Warren, which appeared in James Wan's film The Conjuring (2013), played by Patrick Wilson and Vera Farmiga.

This film marked Leigh Whannell's directorial debut.

Lin Shaye, Leigh Whannell and Angus Sampson were the only actors to appear in all three "Insidious" films.

This film is a prequel to the first Insidious (2010) film, set after Josh Lambert's childhood and before his son, Dalton's, haunting.

Leigh Whannell, who acts and directs this entrée into the "Insidious" franchise, had worked quite often in the horror genre. Amongst his works are Saw (2004), which in addition to writing, he also acted in as well.

Writer/Director Leigh Whannell told casting that he wanted The Man Who Can't Breath to look like the sloth victim in Se7en (1995). The same actor, Michael Reid MacKay, was cast for the role.

Producer Jason Blum has said they were already prepping the early stages for Insidious: Chapter 3 (2015) while promoting the second film.

(at around 28 mins) The book Quinn is reading during the knocking scene is "A Clockwork Orange" by Anthony Burgess.

Stefanie Scott starred in her co star Hayley Kiyoko 's music video, "girls like girls", and the two would also collaborate in the same year again in the film Jem and the Holograms (2015).

Unlike the first two "Insidious" films, in which both father and son Lambert astral projected in their dream state, the demons who attack Quinn Brenner come after her after she attempted to make contact with her deceased mother.

The Wheezing Demon is the only antagonist who has not appeared once in the previous movies nor share any connection to the Lambert family.

The buildings which Quinn, Alex and Sean live in is the same apartment building used in The Butterfly Room (2012), starring Barbara Steele.

On Specs' (Leigh Whannell)'s jacket, the logo of Casper (1949), the iconic friendly ghost, can be seen.

Feature film debut of Hayley Kiyoko, who had previously only been in made-for-television projects.

YouTube personality Joey Graceffa filmed a role for the film, of a psychotic Vietnam veteran, which was left on the cutting room floor.

This film marked the first film since 2006 in which film distributor, Gramercy Pictures, had released a picture.

Actors Dermot Mulroney and Ele Keats had worked together in the film There Goes My Baby (1994), which was shot in 1991.

The play that Stefanie Scott's character Quinn reads from, ('I'll never forget this...you'll go to the end of the world and you'll find me waiting there,') has the co-producer's name, Bailey Conway, on the front as author.

Corbett Tuck, who played the nurse Adele and a Doll Girl ghost in the first film, returns to play a character named Danielle, though it is unknown if they are supposed to be the same character.

Despite being franchise staples and receiving third and fourth billing respectively, Angus Sampson (Tucker) and Leigh Whannell (Specs) don't appear in the film until an hour and one minute in.

Elise refers to him as a "demon." However, his appearance is somewhat more human compared to the Lipstick-Face Demon, whose appearance is more monstrous. This suggests that he is in fact a ghost and not a true demon. This could simply be a form of expression on Elise's part.

Director James Wan and Leigh Whannell both worked on other horror film franchises, including the Saw (2004) franchise.

During the filming of the climax, director Leigh Whannell did not want the other actors (including Lin Shaye and Angus Sampson) to meet the actress playing Lillith, so they could have a more powerful reaction to her appearance. Actress Ele Keats did not step into the set until the very last second.