This was Ben Affleck's biggest paycheck to date, earning him approximately $15 million. Whenever he's asked to why he starred in the film, he responds "The answer lies in the title".
John Woo originally did not want to do his trademark "Mexican Standoff" in this film, but Ben Affleck begged Woo to include the scene, having been a big fan of Woo's films The Killer (1989) and Hard Boiled (1992).
Jennings (Ben Affleck) was supposed to be a New York Mets fan (or Yankees, sources differ), but Affleck, a Boston Red Sox fan, persuaded director John Woo to change the team to the Red Sox.
About the final product and the movie's reception, John Woo said: "I was fine with the sci-fi in Paycheck because there wasn't too much. I had intended to make an Alfred Hitchcock-style movie out of it, something more about suspense and thrills than guns and shooting, but unfortunately the script wasn't written that way. It didn't work well for the suspense, and it didn't come out the way I wanted it to be, not as Hitchcockian. But at least it was nice working with Ben Affleck.''
Matt Damon was originally considered for the part of Michael Jennings, but turned it down, because it was too similar to The Bourne Identity (2002).