Online Gambling on sports is the general activity of predicting sports results by making a bet on the outcome of a sporting event. Perhaps more than other forms of online gambling, the legality and general acceptance of betting on sports vary from nation to nation.

In North America, for example, online gambling on sports is generally forbidden, while in many European nations, bookmaking is regarded as an honorable occupation and, while highly regulated, is not criminalized.

Proponents of legalized sports betting generally regard it as a hobby for sports fans that increases their interest in particular sporting events, thus benefiting the leagues, teams and players they bet on through higher attendances and television audiences.

 Opponents fear that, over and above the general ramifications of online gambling, it threatens the integrity of amateur and professional sport, the history of which includes numerous attempts by sports gamblers to fix matches, although defenders counter that legitimate bookmakers will invariably fight corruption just as fiercely as governing bodies and law enforcement do..

Aside from simple bets, online gambling is commonly done through a bookmaker. Legal sports bookmakers exist throughout the world. In areas where online gambling on sports is illegal, bettors usually make their sports wagers with illicit bookmakers, where thousands of online bookmakers accept bets on sporting events around the world.

 The bookmaker earns a commission of normally ten percent on all losing bets, and pays out a predetermined amount to winning bets.

Bookmakers generally offer two types of wagers on the winner of a sporting event: a straight-up or money line bet, or a point spread wager. Money lines and straight-up prices are used to set odds on sports such as soccer, baseball and hockey as well as individual vs. individual matches, like boxing.

For these sports, bookmakers in Europe and Asia generally use straight-up odds, which are quoted based on a payout for a single bet unit; for example, a 2-1 favorite would be listed at a price of 1.50 dollars, whereas an underdog returning twice the amount wagered would be listed at a price of 3 dollars.