A bookmaker, bookie, or turf accountant is an organization or a person that accepts and pays out bets on sporting and other events at agreed-upon odds.

The first bookmaker, Harry Ogden, stood at Newmarket in 1795, although similar activities had existed in other forms earlier in the eighteenth century.

Following the Gaming Act 1845, the only gambling allowed in the United Kingdom was at race tracks. The introduction of special excursion trains meant that all classes of society could attend the new racecourses opening across the country. Runners working for bookmakers would collect bets in clock bags. Cash flowed to the bookmakers who employed bodyguards against protection gangs operating within the vast crowds. Illegal betting shops were fined, but some, like Bella Thomasson, ran betting businesses that the police appeared to turn a blind eye to.

Bookmakers in many countries focus on accepting bets on professional sports, especially horse racing and association football or Indian Premier League cricket. However, a wider range of bets, including on political elections, awards ceremonies such as the Oscars, and novelty bets are accepted by bookmakers in some countries.

By "adjusting the odds" in their favour (paying out amounts using odds that are less than what they determined to be the true odds) or by having a point spread, bookmakers aim to guarantee a profit by achieving a 'balanced book', either by getting an equal number of bets for each possible outcome or (when they are offering odds) by getting the amounts wagered on each outcome to reflect the odds. When a large bet comes in, a bookmaker may also try to lay off the risk by buying bets from other bookmakers. Bookmakers do not generally attempt to make money from the bets themselves but rather by acting as market makers and profiting from the event regardless of the outcome. Their working methods are similar to those of an actuary, who does a similar balancing of financial outcomes of events for the assurance and insurance industries.

In 1961, Harold Macmillan's Conservative government legalised betting shops, with tough measures enacted to ensure that bookmakers remained honest. A large industry has grown since. At one time, there were over 15,000 betting shops. Now, through consolidation, they have been reduced to between 9,100 and 9,200 in 2013. This number has reduced further to 6,219 as of March 2022, largely as a result of Covid-19 and the forced closure of shops on the UK high street. The group of the largest bookmakers in the country, known as the "Big Three", comprises William Hill, Ladbrokes, and Coral.

The United Kingdom's Gambling Act 2005 introduced a new regulatory system for governing gambling in Great Britain. This system includes new provisions for regulating the advertising of gambling products. These provisions of the Act came into effect in September 2007. It is an offence to advertise in the UK, gambling that physically takes place in a non-European Economic Area (EEA) or, in the case of gambling by remote means, gambling that is not regulated by the gambling laws of an EEA state. The Gambling Commission is the body that makes sure all sites and operators follow the new restrictions. In addition to the Gambling Act of 2005, according to the new gambling bill, online gambling sites are only allowed to offer services within the United Kingdom, if they are registered at the UK Gambling Commission.

Improved TV coverage and the modernisation of the law have allowed betting in shops and casinos in most countries. In the UK, on-track bookies still mark up the odds on boards beside the racecourse and use tic-tac or mobile telephones to communicate the odds between their staff and to other bookies, but, with the modernisation of United Kingdom bookmaking laws, online and high street gambling are at an all-time high. A so-called super-casino had been planned for construction in Manchester, but the government announced that this plan had been scrapped on 26 February 2008.