The rules of billiards are regulated by international billiards associations to guarantee a consistent game across the world. Because billiards had many origins and differences of play across geographic distances, it was essential for play to be regulated internationally. The World Pool Billiard Association is the international association, and the Billiards Congress of America regulates tournament play in the United States. With billiards having a rich history across the world, it is interesting that the World Pool Billiard Association is quite new and that international rules are a recent addition to the sport. With active localized organizations such as the Billiards Congress of America and the European Pocket Billiard Federation it was not until 1990 that a true worldwide set of rules were established.

The World Pool Billiard Association and the Billiard Congress of America do not only regulate the play of the game, but also regulate and standardize the equipment. As in other professional sports, the use of standard equipment reduces the possibility of an unfair advantage through differences in equipment.

There are several varieties of cue sport games, with specific rules for each. In the United States 8-ball and 9-ball are the most popular games. The first worldwide tournament was a 9-ball game, which has become a popular annual event. The standardization of the rules of billiards has helped this game grow and increase competition on a worldwide level.

The official rules of billiards can be found on the web sites for the World Pool Billiard Association and the Billiard Congress of America. The rules cover such items as appropriate sportsmanlike conduct to defining a foul. Each variety of the game has the specific rules as well as general rules that apply to all regulated cue sports. There are also rules outlined for players with disabilities. Having an international set of rules helps to keep the playing field fair for all players.

Look at this source for the official rules.