Betfair is the world's largest Internet betting exchange. The company is based in Hammersmith in West London, England. In 2011 Betfair went offshore and was registered and licensed in Gibraltar and since 9 March 2011 its betting exchange operate under this offshore licence. Since Betfair was launched in June 2000 it has become the largest online betting company in the UK and the largest betting exchange in the world. Betfair claim to have over 4 million customers and a turnover in excess of £50 million a week. The company employs about 2300 people worldwide and 1200 in the UK.

A betting exchange allows gamblers to bet at odds set and requested by other punters rather than by a bookmaker. Members can make both "back" bets (normal bets on a selection to win) and "lay" bets (bets on the opposite side of the Back, against the selection), thereby eliminating the traditional bookmaker.

Betfair claims on average 20 percent better odds than those offered by a traditional bookmaker. Betfair charges a commission on all winning bets, which is set at 5 percent of the net winnings for most markets, although according to how much a client wagers on the site, it is possible to reduce the amount of commission paid to as low as 2 percent.