What game do the M.I.T. students play to win in the movie "21"?

What game do the M.I.T. students play to win in the movie 21? They play blackjack, using card counting to improve their odds.

The 2008 film 21 follows Ben Campbell and fellow Massachusetts Institute of Technology students who join a secretive team that travels to Las Vegas. Their goal is not simply to gamble randomly: they track the cards that have already been dealt and use probability to estimate when the remaining deck favors the player. The group also uses coded signals and disguises to avoid attracting casino security's attention.

The movie was inspired by Ben Mezrich's book Bringing Down the House, which dramatized the real MIT Blackjack Team. In both the film and the real-world story, blackjack is central because the player's decisions and the composition of the remaining deck can affect the house edge. Casinos generally do not treat card counting as criminal cheating, but they can bar suspected counters from playing.

A common mistake is to answer poker, roulette, or baccarat because those are also associated with casinos. The students in 21 specifically target blackjack, and the title refers to the game's goal of reaching 21 without going over.