Japanese or Riichi Mahjong is a specific variant of the traditional Chinese Mahjong game. Players draw and discard tiles of different suits and values to build valid Mahjong hands. A valid Mahjong hand generally consists of 14 tiles: 4 sets and a pair, where the sets can be sequences in the same suit or triplets. Sets can be completed not only by drawing appropriate tiles but also by claiming discarded tiles.

The game takes its depth from the intricate scoring system and the fact that all discarded tiles are open. 'Riichi' (called out by players) is referring to one of these intricate elements: placing a bet on winning a concealed hand. Japanese Mahjong blends elements of mostly luck-based hand-building games like Rummy with a heavy dose of strategy. In particular, the scoring system dictates that offensive and defensive play must both be mastered. Knowledge of hand values, pattern recognition skills, and the continuous analysis of your opponents' discards are key elements for success in this game.

Japanese Mahjong is played extensively, including professionally, in Japan. The European Mahjong Association (EMA) is the de facto governing body for play in Europe, and this implementation follows the current set of EMA rules (2016 version).