The central game of Deal or No Deal involves a contestant, a banker, and a host/presenter who emcees the game. The game revolves around the opening of a set of numbered briefcases (or boxes), each of which contains a different prize (cash or otherwise). The contents of all of the briefcases are known at the start of the game, but the specific location of any prize is unknown. The value of each of the boxes or briefcases is indicated by a label or card sealed within it.
The contestant claims (or is assigned) a briefcase to begin the game. The case's value is not revealed until the conclusion of the game.
The contestant then begins choosing cases to be removed from play. The amount inside each choice is immediately revealed; by process of elimination, the amount revealed cannot be inside the player's chosen case. Throughout the game, after a predetermined number of cases have been opened, the banker offers the contestant an amount of money and/or prizes to quit the game, the offer based roughly on the amounts remaining in play and the contestant's demeanor. The player then answers the titular question, choosing:
"Deal", accepting the offer presented and ending the game, or
"No Deal", rejecting the offer and continuing the game.
This process of removing cases and receiving offers continues, until either the player accepts an offer to 'deal', or all offers have been rejected and the values of all unselected cases are revealed. The player wins the value of the deal taken, or if no deal is taken, the contents of the player's case.
Should a player end the game by taking a deal, a pseudo-game is continued from that point to see how much the player could have won by remaining in the game. Depending on subsequent choices and offers, it is determined whether or not the contestant made a "good deal", i.e. won more than if the game were allowed to continue.