method of wagering introduced in France about 1870 by Parisian businessman Pierre Oller. It became one of the world's most popular methods of betting on horse (horse racing) races.

Most pari-mutuel systems are operated by the racetrack, although in France a national pari-mutuel system with offtrack branches was established in 1891. In pari-mutuel betting, the player buys a ticket on the horse he wishes to back. The payoff to winners is made from the pool of all bets on the various entries in a race, after deduction of an operator's commission and tax. The system has the advantages of always giving the operator a profit and allowing any number of bettors to win.

An important innovation in pari-mutuel betting came in the 1920s with the development of the totalizator, a mechanical device for issuing and recording betting tickets. Modern totalizators, usually computers, calculate betting pools and current odds on each horse and flash these figures to the public at regular intervals. They may also display race results, payoff amounts, running times, and other information. Increasingly sophisticated equipment has encouraged introduction of a variety of combination bets, such as the daily double (picking winners in two specified races, usually the first two), exacta, or perfecta (picking the first two finishers in a race in precise order), quinella (picking the first two finishers in a race regardless of order), and pick six (picking the winners in six consecutive races, usually the second through the seventh).

Pari-mutuel betting is still most practiced in horse racing but has an important place in other sports as well, most notably dog racing and jai alai.