Deal or No Deal is a television game show format owned by Dutch-based production company Endemol, known for creating such shows as Big Brother. The basic format of Deal or No Deal consists of a number of cases (usually 26) each containing a different amount of money. Not knowing the sum of money in each case, the contestant picks one case which potentially contains the contestant's prize. They then open the remaining cases, one by one, revealing the money they contained. At predetermined intervals the contestant receives an offer from the bank (run by "The Banker") to purchase the originally chosen case from the contestant, the offer being based on the potential value of the contestant's case. The contestant must then decide whether to take the deal from the bank, or to continue opening briefcases. If the contestant decides not to take the deal and reveals low value cases, then the next bank offer is likely to be higher (as the contestant's case is proven not to contain these low values). Alternatively, there is risk in revealing higher values, lowering future offers from the bank. This feature makes for an exciting suspense game.

The format of Deal or No Deal varies in each country. In the UK, for example, contestants choose from 22 boxes rather than 26 briefcases. The concept of pitting a contestant against an in-house adversary (in this show, the bank) is unusual, though not unique, among game shows.