Betfair is a betting exchange. It is the world's largest by some considerable margin. This it has achieved from a standing start in 2000. It is perhaps Europe's most successful e-business measured by turnover - reputed to be £65million ($100m) per week - or profitability.
The writer is an enthusiastic user of Betfair's service. Much better odds can be found here than at any high street bookmaker. A result can be layed as well as backed. Typically a bookmaker only allows a horse to be backed - not layed. As on other betting exchanges one is allowed to offer one's own odds to others.
The deepest and most liquid markets are UK horse racing and UK soccer. But USA horse racing, American football, world soccer, cricket, tennis and rugby are amongst the other markets covered.
Users can participate from around the world but US residents as well as residents of other
countries may be breaking local laws by taking part.
Those sick and tired of being ripped off by their bookmaker with their usurous overround should vote with their feet.
Betfair's dominance over other betting exchanges seems unassailable but competition includes
Betdaq and Play121.