Mahjong (/mɑːˈdʒɒŋ/ mah-JONG, Mandarin: [mǎ.tɕjâŋ]) is a tile-based game that was developed in China during the Qing dynasty 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 Japan, South Korea and Southeast Asia). The game and its regional variants are widely played throughout Eastern and South Eastern Asia and have become popular in Western countries too. The game has also been adapted into a widespread online entertainment. Similar to the Western card game rummy, Mahjong is a game of skill, strategy, and calculation and 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 4 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.

In Chinese, the game was originally called 麻雀 (pinyin: máquè)—meaning sparrow—which is still used in some southern dialects. It is said that the clacking of tiles during shuffling resembles the chattering of sparrows. It has also been suggested that the name came from an evolution of an earlier card game called Madiao which mahjong tiles were adapted from. Most Mandarin-speaking Chinese now call the game 麻将 (májiàng). Its name is similar in other languages, except in Thai, where it is called ไพ่นกกระจอก (phai nok krachok), a calque meaning "sparrow cards."

There are many highly varied versions of mahjong both in rules and tiles used. "Old Hong Kong Mahjong" uses the same basic features and rules as the majority of the different variations of the game. This form of Mahjong uses all of the tiles of the most commonly available sets, includes no exotic complex rules, and has a relatively small set of scoring sets/hands with a simple scoring system. For these reasons Hong Kong mahjong is a suitable variation for the introduction of game rules and play and is the focus of this article.