Key differences between the American version of mahjong and Asian variations include the greater number of tiles, the inclusion of jokers and the Charleston. There isn't an official Asian version of mahjong, as several variations exist, including Chinese classical mahjong, Japanese mahjong and Korean mahjong.
Standard American mahjong sets come with 152 tiles, whereas Chinese sets typically have 144 tiles. The required amount of tiles varies depending on the variation, but 136, 144 and 152 tiles are all commonly used.
Joker tiles are common in American mahjong, although they are also included in other variations. Jokers are wild cards, although rules about how they can be used vary. In standard American mahjong, a player can use a joker as a substitute for any tile, as long as it's included in a group of three or more.
The Charleston is a tile exchange that occurs before each hand. Players pass three tiles to the right, three across and three to the left. This first Charleston is required for every player. If all the players agree, a second Charleston then occurs. If any player doesn't agree, it doesn't occur.
After the first or second Charleston, depending on how many the players performed, players sitting across from one another may perform a courtesy Charleston. They exchange one, two or three tiles.