Senior math major Ben Campbell (Jim Sturgess) of Massachusetts Institute of Technology (MIT) is accepted into Harvard Medical School, but cannot afford the $300,000 fee. Despite a 44 MCAT score and top grades, Ben faces fierce competition for the prestigious Robinson Scholarship that would pay for medical school in its entirety. The director tells him that the scholarship would go to the student who "dazzles" him. Ben did not have anything to dazzle the director then, so he walks away, trying to write an essay with nothing in mind to compose it.
At MIT, professor Micky Rosa (Kevin Spacey) challenges Ben with the Monty Hall problem in one of his non-linear equation classes, which he solves successfully. After looking at Ben's score on his latest non-linear equations paper, on which he got 97%, Rosa invites Ben to join his blackjack team, which consists of fellow students Choi, Fisher, Jill, and Kianna. Despite being told by Rosa that he had already gotten into the Harvard Medical School, Ben refuses to join the team on the premise he had been promoted at his job. Next day, Jill visits Ben at his job and attempts to coax him into joining the team. The system involves card counting, and the team is split into two groups. "Spotters" play the minimum bet and keep track of the count. They send secret signals to the "big players", who place large bets whenever the count at the table is favorable. Ben reluctantly joins the team, telling Rosa he is only doing so until he can pay for medical school.
Rosa takes the team to Las Vegas over many weekends; Ben comes to enjoy his luxurious lifestyle as a "big player" there. His performance impresses Jill—who develops a mutual attraction with him—and Rosa. However, Fisher becomes jealous of Ben's blackjack success. Rosa kicks a drunken Fisher out of the team after he insults Ben and incites a melee, requiring the team to scramble to cash in their stock of chips before the casino swaps out (a common practice after a fight). Meanwhile, security chief Cole Williams (Laurence Fishburne) monitors the blackjack team, having his eyes on Ben.
Ben, distracted by blackjack, does not complete his part of a project for an engineering competition, estranging him from his pre-blackjack friends. During the next trip to Vegas, an emotionally distracted Ben continues playing even after he is signaled to walk away, thereby losing 200,000 dollars. Angered and upset, Rosa leaves the team and demands that Ben repay him for the loss. Rosa told him the reason why he lost, he wasn't counting, he was gambling. Jill asks how much Ben made in his winnings and Ben informs her that it is over 300,000 dollars and that he does not intend to stop. Ben and his three remaining teammates agree to go into business for themselves; Williams, however, kidnaps Ben, beats him and frees him after being tipped off by Rosa.
Ben learns that he has been given an incomplete in one of his classes and, therefore, will not graduate, and that his winnings have been stolen from his dormitory room. He suspects that Rosa is behind the events but has no evidence. Ben reconciles with his friends and Jill, and approaches Rosa with an offer: he and the team will hit Vegas for another attempt before the casinos install a biometric software that will quickly identify card counters, as long as Rosa, once a very successful "big player", also plays.
Disguised, the team returns to Planet Hollywood and wins $640,000 before fleeing from Williams and his men, chips in hand. Ben and Rosa split up, with Rosa taking the bag of chips. Rosa escapes into a limousine with the intention of stealing the winnings, but finds his bag is full of chocolate coins and that the casino manager is driving Rosa's limousine.
It is revealed that Williams had made a deal with Ben after beating him up: he would let Ben come to Vegas for one night to make a lot of money gambling in exchange for Rosa. Rosa had won a seven-figure sum at Williams's casino by counting cards, a feat that cost Williams a pit boss job. After capturing Rosa, Williams confronts Ben and demands at gunpoint the bag of chips for his retirement; after giving up the money, Ben rejoins his friends and pre-blackjack friends, who have, in fact, been counting all night themselves. The film closes with Ben recounting the entire tale to a "dazzled" Harvard director.Jim Sturgess as Ben Campbell
Kevin Spacey as Professor Micky Rosa
Kate Bosworth as Jill Taylor
Laurence Fishburne as Cole Williams
Aaron Yoo as Choi
Liza Lapira as Kianna
Jacob Pitts as Fisher
Jack McGee as Terry
Josh Gad as Miles Connoly
Sam Golzari as Cam Azazi
Helen Carey as Ellen Campbell
Jack Gilpin as Bob Phillips
Spencer Garrett as Stemple
Jeff Ma (as Jeffrey Ma) as Planet Hollywood Dealer Jeff (the person upon whom the story was based).
Kris Williams as Jill's Friend
Kieu Chinh as Poker player
The filming of 21 began in March 2007. Principal filming of the Las Vegas scenes took place at the Planet Hollywood Casino, the Red Rock Casino, and the Hard Rock Casino in Las Vegas. Filming also took place at Harvard Medical School, Chinatown, in Cambridge, and the Christian Science Center in Boston, Massachusetts. As MIT did not allow filming on campus, the MIT school and dorm interiors, the gymnasium, and the alumni reception were all shot at Boston University.
21 received mixed reviews from critics. Review aggregator Rotten Tomatoes reported that 36% of 165 critics gave the film a positive review, for an average rating of 5.2/10. The site's critical consensus reads that "21 could have been a fascinating study had it not supplanted the true story on which it is based with mundane melodrama." Metacritic reported the film had an average score of 48 out of 100, based on 29 reviews.
In its opening weekend, the film grossed $24,105,943 in 2,648 theaters in the United States and Canada, averaging $9,103 per venue and ranking first at the box office. The film was also the number one film in its second weekend of release, losing 36% of its audience, grossing $15,337,418, expanding to 2,653 theaters, and averaging $5,781 per venue. The film dropped to third place in its third weekend, losing 32% of its audience, grossing $10,470,173, expanding to 2,736 theaters, and averaging $3,827 per venue. By the fourth weekend it fell to sixth place, losing 47% of its audience, grossing $5,520,362 expanding to 2,903 theaters, and averaging $1,902 per venue.
By the end of its theatrical run, the film grossed a total of $157,802,470 worldwide — $81,159,365 in the United States and Canada and $76,643,105 in other territories, against a budget estimated at $35 million.
A race-based controversy arose over the decision to make the majority of the characters white Americans, even though the main players in the book Bringing Down the House, upon which the film 21 is based, were mainly Asian-Americans. The lead role was given to London-born Jim Sturgess, who required a dialect coach to speak with an American accent.
Jeff Ma, who was the real-life inspiration for the character Ben Campbell and served as a consultant on the film, was attacked as being a "race traitor" on several blogs for not insisting that his character be Asian-American. In response, Ma said, "I'm not sure they understand how little control I had in the movie-making process; I didn't get to cast it." Ma said that the controversy was "overblown" and that the important aspect is that a talented actor would portray him. Ma, who is Chinese American, told USA Today, "I would have been a lot more insulted if they had chosen someone who was Japanese or Korean, just to have an Asian playing me."
Nick Rogers of The Enterprise wrote, "The real-life students mostly were Asian-Americans, but 21 whitewashes its cast and disappointingly lumps its only Asian-American actors (Aaron Yoo and Liza Lapira) into one-note designations as the team's kleptomaniac and a slot-playing 'loser.'"
The Media Action Network for Asian Americans (MANAA) reported on their web site: "After the ‘white-washing’ issue was raised on Entertainment Weekly’s web site,  producer Dana Brunetti wrote: "Believe me, I would have LOVED to cast Asians in the lead roles, but the truth is, we didn’t have access to any bankable Asian-American actors that we wanted."
21 was released on DVD and Blu-ray in Region 1 on July 22, 2008.
In pre-production, the producers and the book's original writers predicted that the Vegas casinos would be unhelpful, as a film that told viewers the basics of card counting might hurt their bottom line. A featurette included with the DVD completely and accurately describes the "Hi-Lo" system used by the MIT Blackjack Club and by Rosa's team in the film.
In fact, the writers were surprised when told by the producers that MGM Studios would finance the film, though all "MGM" casinos (including one used by the real MIT Blackjack Team) are owned by MGM Resorts International and are no longer related to MGM Studios. In reality, as another DVD featurette reveals, the casinos (including MGM Resorts) saw the film as an attention-getter; people who saw it would be encouraged to go to Vegas and play: some just for fun and some attempting to count cards but failing to learn or memorize the entire strategy or making too many mistakes. The film withheld critical strategy details (such as the conversion from the "running count" to a "true count"), and most beginning card counters underestimate the number and value of the mistakes they make.
The soundtrack was released at the same time as the film.
Although it is not included in the soundtrack, Moby's "Slippin' Away" (Axwell Vocal Remix) plays in the scene when Ben is passing through airport security.
The song "Everybody Get Dangerous" by Weezer was also featured in the film, but not included on the soundtrack since it was not yet released. It would later be released on Weezer's new record, The Red Album. It is played on a distant radio when the team is in a poker club.
The songs "I Want You to Want Me" by Cheap Trick and "Music is Happiness" by The Octopus Project were also featured in the film but not on the soundtrack album.
The song "Magnificent" by Estelle (feat. Kardinal Offishall) was also featured in the film but not on the soundtrack album. It's played approximately 58 minutes in, after the Weezer song, in the scene where Ben buys Jill a beer. It's subtle, and has a reggae beat.
In the promotional trailers, "Break on Through (To the Other Side)" by The Doors was used.
During the restaurant scene where the team explains to Ben how they work, "Home" by Great Northern can be heard playing in the background.
The song "Again with the Subtitles" by Texas artist Yppah is another uncredited song in the film.
The track played as the team makes off at the end of the film is "Rito a Los Angeles" by Giuseppe De Luca, which features part of the main riff of "In-A-Gadda-Da-Vida". This track is also used in Ocean's Twelve, the first sequel to the caper film Ocean's Eleven, about actually robbing casinos in Vegas.
My Mathematical Mind by Spoon was featured in the trailers.
- The Rolling Stones—"You Can't Always Get What You Want" (Remixed by Soulwax) (6:07)
- MGMT—"Time to Pretend" (Super Clean Version) (4:20)
- LCD Soundsystem—"Big Ideas" (5:41)
- D. Sardy featuring Liela Moss—"Giant" (3:42)
- Amon Tobin—"Always" (3:38)
- Peter Bjorn and John—"Young Folks" (4:37)
- Shook One —"Soul Position" (4:16)
- Get Shakes—"Sister Self Doubt" (4:22)
- The Aliens—"I Am The Unknown" (5:27)
- Rihanna—"Shut Up and Drive" (3:34)
- Knivez Out—"Alright" (3:31)
- Domino—"Tropical Moonlight" (3:28)
- Unkle—"Hold My Hand" (4:58)
- Mark Ronson featuring Kasabian—"L.S.F. (Lost Souls Forever)" (3:32)
- Broadcast—"Tender Buttons" (2:51)