Although set in the then-present day, i.e. 2007/8, the film is based on teams active between 1979 and 1994. And at one point, more than 80 players were on the original MIT team.
According to Kevin Spacey, as part of their research for the film, they took some of the real players who were on the original team to Vegas. Although they weren't allowed to play, every time they wanted Spacey to up his bet, they would push up against his chair. He said, "I would win every time!"
The main characters upon which the film 21 is based were Asian. Controversially, mostly Caucasian actors were cast. Jim Sturgess required a dialect coach to speak with an American accent.
The movie was used as a luxury prize for the contestants on the Big Brother (2000) 9 in the US. They played a competition involving blackjack, and the winners got to see a special advance screening of the movie. One contestant won a trip to Las Vegas worth $21,000, which included a three night stay at the same hotel the actors from the movie stayed in.
Boston University students were used as extras in many of the classroom scenes.
Jeff Ma: The real-life inspiration behind the character Ben Campbell as a Planet Hollywood blackjack dealer, referred to by Ben Campbell as 'my brother from another mother'.
Gustaf Skarsgård: Long-haired man working for Cole Williams. He can be seen chasing Ben in the final run out of the casino.