Why does mahjong have different sets of rules?

Mahjong has different sets of rules because of regional variations, such as American, Chinese, Hong Kong, European Classical and Taiwanese. The Riichi competition version, also known as Japanese modern, is typically used in tournaments.

Many similarities exist among the rules for versions of mahjong. Differences among styles include which tiles are allowed in play and how many tiles are in a hand.

In China, mahjong is played many different ways, but the China's State Sports Commission codified an official version that includes components from its variations. The Hong Kong or Cantonese setup is highly popular, while the European classical version is seldom played in China.