- Cut Song: Weezer recorded an acoustic version of "Happy Together" to be included in the film. However, Spike Jonze felt the original version by The Turtles was a better fit for the film.
- There exists a movie called Thr3e that has a remarkably similar premise to Donald Kaufman's (fictional) script "The Three". (There's no chase scene with a horse and a motorcycle, though.) Amazingly enough, though, its similarity was entirely coincidental.
- It's not all that surprising when you think of how bland and cliche Donald's story was, which the film was entirely aware of. Of course there would be several psychological thrillers using the same or very similar concept without the writers even having heard of Adaptation.
- Identity has an extremely similar twist to The Three, with the added bonus that it has multiple serial killers, multiple cops, and multiple damsels in distress all running concurrently and on different levels of reality.
- Deleted Role: Though his name appears in the final credits, Stephen Tobolowsky doesn't appear in the movie, since all of his scenes were cut.
- Dyeing for Your Art: To portray John LaRoche, Chris Cooper grew out his hair, shed weight and used a prosthesis to create the illusion of a toothless mouth. Spike Jonze granted Cooper's request for numerous takes so he could find the right tone for the eccentric character.
- Flip-Flop of God: God in this case being Charlie, who says he'll never pack his screenplays with sex, drugs and violence...but just look at the third act of the film.
- Playing Their Own Twin: Nicolas Cage plays Charlie and his twin brother Donald.
- Talking to Himself: Nicolas Cage as Charlie and Donald Kaufman.
- What Could Have Been:
- Tom Hanks was originally cast in the lead role(s) but dropped out.
- Joaquin Phoenix auditioned for the role of John LaRoche and got close to getting the part. According to Spike Jonze, during one of their final meetings, Phoenix told him that he was wrong for the part, and that it should go to someone else, and took himself out of the running. Chris Cooper eventually got the part, and ended up winning an Oscar for his performance.
- In the original script, there was a cryptid known as the Swamp Ape that kills John Laroche at the climax. Robert McKee asked that the Swamp Ape be removed, saying "I'll be a character in a movie but I won't be a character in a bad movie". Susan Orlean was also supposed to die by shooting herself with Laroche's rifle.
Trivia / Adaptation.