Tom Cruise wanted to do another spy thriller, but he thought Salt (2010) and The Tourist (2010) were too similar to his Mission: Impossible (1996) franchise. He ultimately chose this project once it became an espionage thriller with comic elements.
The film's production partners, New Regency and Dune Entertainment, offset financing for the film by paying Tom Cruise a lower advance fee than he normally received. According to the Los Angeles Times, Cruise received $11 million for Knight and Day (2010), not the $20+ million he usually receives.
While leads Cruise and Diaz were promoting this movie they both appeared on the BBC's Top Gear Top Gear: Episode #15.5 (2010) where they competed in the traditional speed lap in the "reasonably-priced car." Their respective time records were 01m:44.2s and 01m:45.2s.
There are two references to Tom Cruise's other films. One being when Roy lands the plane the truck driver is singing "Rock You Like A Hurricane" which is a song Tom Cruise's Character sings in Rock of Ages. The other is when Roy saves June from the car chase and Cruise's character says "you're an excellent driver June" referencing the film Rain Man. Where Dustin Hoffman's character always says he is "an excellent driver".