Mahjong is a tile-based game that was developed during the Qing dynasty in China and has spread throughout the world since the early 20th century. It is commonly played by four players (with some three-player variations found in JapanSouth Korea, and Southeast Asia). The game and its regional variants are widely played throughout Eastern and South-Eastern Asia and have also become popular in Western countries. The game has also been adapted into widespread online entertainment. Similar to the Western card game rummy, Mahjong is a game of skill, strategy, and calculation, and it involves a degree of chance.

The game is played with a set of 144 tiles based on Chinese characters and symbols, although some regional variations may omit some tiles or add unique ones. In most variations, each player begins by receiving 13 tiles. In turn players draw and discard tiles until they complete a legal hand using the 14th drawn tile to form four melds (or sets) and a pair (eye). A player can also win with a small class of special hands. There are fairly standard rules about how a piece is drawn, how a piece is robbed from another player, the use of simples (numbered tiles) and Honors (winds and dragons), the kinds of melds allowed, how to deal the tiles and the order of play. Despite these similarities, there are many regional variations to the rules including rather different scoring systems, criteria for legal winning hands, and even private table rules which distinguish some variations as notably different styles of mahjong.