- Box Office Bomb: Budget, $60 million. Box office, $31,165,421 (domestic), $90,565,421 (worldwide).
- Dawson Casting: The film is very guilty of this, casting actors in their mid-to-late-twenties as the teenage main characters. The main protagonists Clary (15) and Jace (17) are being played by Lily Collins and Jamie Campbell Bower, both of whom are 23. Isabelle (16) and Simon (also 16) are being portrayed by 24-year-old actors Jemima West and Robert Sheehan, while most notoriously Alec (18) is being played by 27-year-old Kevin Zegers. That said, the producer has revealed that although they won't be specifying anyone's exact age in the movie, the characters are supposed to be somewhat older than their book counterparts. To make matters even more mind-boggling, the character of Luke (who is pushing forty, and acts as a surrogate father to the kids) is being played by the 28-year-old Aidan Turner.
- Fake American: Irish Robert Sheehan plays the American Simon Lewis.
- Follow the Leader: The film was green-lit as an attempt to fill the void of "teen paranormal romance" films left behind once the last Twilight film was released.
- Promoted Fanboy: Lily Collins was a big fan of the books and made several calls as soon as she heard a movie was being made to get an audition for Clary.
- Romance on the Set: Between Lily Collins and Jamie Campbell Bower.
- Stillborn Franchise: Became one of these after performing poorer than expected at the box office, with production shut down indefinitely on the sequel only a week before it was supposed to start. It was supposedly only a delay requested by the author herself, who was not pleased with the script for the next movie and asked it to be rewritten. In late 2013/early 2014 it looked like progress was being made on the sequel, with both a new production date and several cast members being re-signed on to the film. However in October 2014, it was officially announced that the sequel had officially been cancelled in favour of a TV Show adaptation of the books, starting with a re-adaptation of the first book and continuing with the rest of the series. Of course, even if the film franchise did continue, Godfrey Gao's fatal heart attack in November 2019 would've made for an even greater obstacle.
- Underage Casting: Jonathan Rhys Meyers, who was in his mid-thirties at the time, plays the father of Lily Collins's character, despite only being 12 years older than her. The character also claims to be the father of Jace, played by Jamie Campbell Bower, who is just 11 years younger. Meyers wasn't made to look older, either, even outside of flashbacks, so it's noticeable.
- What Could Have Been:
- Alex Pettyfer turned down the part of Jace. Among others who auditioned were Alexander Ludwig, Xavier Samuel, Douglas Booth and Lucas Till before Jamie Campbell Bower won the role.
- Matthew Daddario, who would later play Alec Lightwood in the TV adaptation of the books, auditioned for a part in the film.
Trivia / The Mortal Instruments: City of Bones