- Channel Hop: The film started at Revolution Studios before moving to Sony.
- Dueling Movies: Came out around the same time as Killers and while their plots are not identical, they are similar enough that the general public noticed the oddity of their close release dates. Ultimately, Killers ended up being panned (11% on Rotten Tomatoes) and barely turned a profit at the box office, while Knight and Day received more moderate reviews and grossed $260+ million.
- No Stunt Double: Tom Cruise and Cameron Diaz did a majority of the stunts on their own. Cruise and Diaz are avid drivers, and have experience in doing sharp turns and 180s.
- Uncredited Role: Over twelve writers worked on the film but the Writers Guild of America ruled that only one of them, Patrick O'Neill, should be credited. Some of the other uncredited writers were Scott Frank, Laeta Kalogridis, Ted Griffin, Dana Fox, and Simon Kinberg.
- What Could Have Been:
- Adam Sandler was offered a starring role in the film; he declined, saying, "I just don't see me with a gun."
- The film was going to star Chris Tucker and Eva Mendes.
- Gerard Butler met with production staff regarding starring opposite Cameron Diaz. Butler instead decided to take on the lead role in The Bounty Hunter.
- Working Title: Witchia, Troubled Man.
Trivia / Knight and Day