There are many variations of mahjong. In many places, players often observe one version - and are either unaware of other variations or claim that different versions are incorrect.

Although many variations today differ only by scoring, there are several main variaties:

• Chinese Classical Mahjong is the oldest variety of Mahjong, and was the version introduced to America in the 1920s under various names. It has a small, loyal following in the West, although few play it in Asia.
  
• Hong Kong Mahjong or Cantonese Mahjong is possibly the most common form of Mahjong, differing in minor scoring details with the Chinese Classical variety.
  
• Taiwanese Mahjong is the variety prevalent in Taiwan and involves hands of 16 tiles, as opposed to the 13-tile hands in other versions. It also features bonuses for dealers and recurring dealerships, and allows for multiple players to win from a single discard.
  
• Japanese Mahjong is a standardized form of Mahjong in Japan, found prevalently in video games. In addition to scoring changes, the rules of riichi and dora are unique highlights of Japanese Mahjong.
  
• Western Classical Mahjong is a descendant of the version of Mahjong introduced by Babcock to America in the 1920s. Today, this term largely refers to the Wright-Patterson rules, used in the U.S. military, and other similar American-made variants that are closer to the Babcock rules.
  
• American Mahjong is a form of Mahjong standardized by the National Mah Jongg League and the American Mah-Jongg Association -- and makes the greatest divergence from traditional Mahjong. It uses Joker tiles, the Charleston, plus melds of five or more tiles, and eschews the Chow and the notion of a standard hand. Purists claim that this makes American Mahjong a separate game. In addition, the NMJL and AMJA variations, which differ by minor scoring differences, are commonly referred to as Mahjongg or Mah-jongg (with two Gs, often hyphenated).
  

The number of hands designated in these rules is 81; each hand, depending upon its difficulty, is scored from between 1 to 88 points.

There are no doubling schemes, but rather, the points for each hand are added together in a simple sum. In Official International, there is a minimum of 8 points needed to go Out - for example, one adds the 2 points from All Chows to the 2 points from All Simples, and so on, until he or she has at least 8 points.

One game consists of 4 rounds (East, South, West, North) of 4 games each. Also, 8 flower tiles are used, each scoring 1 point when obtained. However, flower tiles are counted apart from the 8 point minimum - this means that 8 points outside of the flower tiles are necessary to go Out, and also that the flower tiles do not count against the Chicken Hand (which is a hand that otherwise has 0 points).

Points for flower tiles are simply added to the final score after going Out In some forms of Mahjong, the player who discards the winning tile is solely responsible for the payout to the winner. However, in Official International Rules, when the winner goes Out off a player's discard, he or she receives 8 points each from the 3 opponents, as well as a separate payment, equal to the points scored for the value of the hand, from the player who discarded the winning tile. When the hand is self-drawn, add 8 points to the value of the hand.

The winner receives this amount from each of the three opponents.

Rule summary

1. Eighty-one different hands, each assigned a value of 1- 88.
2. Minimum 8 points to go out.
3. One game consists of 4 rounds (16 hands).
4. Use a simple sum to calculate combinations of hands.
5. Japanese "Reach" rule is not included.
6. Dealer does not receive additional payment when winning, nor repeat his or her deal.
7. No "Sacred Discard" rules apply. A player may go out on a tile that he or she has previously discarded. A player may claim an already-completed Chow or Pung and discard the remaining portion of it (for example, holding 2-3-4 and then claiming 1 to change the already-completed Chow to 1-2-3, then discarding the 4. For Pungs, it is acceptable to hold 8-8-8, steal the last 8 to create 8-8-8 again, and then discard the remaining 8.).
8. All Chows hand can finish with any type of Wait
9. A player goes out by announcing "hu" (Mandarin Chinese, 2nd tone) and revealing his or her hand.
10. No Dead Tiles will be designated. Play continues until the last tile has been used.