Greyhound racing is the sport of racing greyhounds. The dogs chase a lure (traditionally an artificial hare or rabbit) on a track until they arrive at the finish line. The one that arrives first is the winner.

In many countries, greyhound racing is purely amateur and conducted for enjoyment. In other countries (particularly the UK, US, Ireland and Australia), greyhound racing is a popular form of gambling, similar to horse racing. There is some popular concern in the aforementioned countries regarding the well-being of the dogs; the effectiveness of industry efforts to address these concerns is controversial. A greyhound adoption movement has arisen to assist retired racing dogs in finding homes as pets.
Modern greyhound racing has its origins in coursing. The first recorded attempt at racing greyhounds on a straight track was made beside the Welsh Harp reservoir, Hendon in 1876, but this experiment did not develop. The sport emerged in its recognizable modern form, featuring circular or oval tracks, with the invention of the mechanical or artificial hare in 1912 by Owen Patrick Smith. O.P. Smith had altruistic aims for the sport to stop the killing of the jack rabbits and see "greyhound racing as we see horse racing". The certificates system led the way to parimutuel betting, as quarry and on-course gambling, in the United States during the 1920s. In 1926, armed with the Smith patents and a hand shake, it was introduced to Britain by an American, Charles Munn, in association with Major Lyne-Dixon, a key figure in coursing, and a Canadian, Brigadier-General Critchley. The deal went sour with Smith never hearing from Munn again. Like the American, International Greyhound Racing Association, the In.G.R.A. Munn and Critchley launched the Greyhound Racing Association, and held the first British meeting at Manchester's Belle Vue. The sport was successful in cities and town throughout the U.K. - by the end of 1927, there were forty tracks operating. The sport was particularly attractive to predominantly male working-class audiences, for whom the urban locations of the tracks and the evening times of the meetings were accessible, and to patrons and owners from various social backgrounds. Betting has always been a key ingredient of greyhound racing, both through on-course bookmakers and the totalisator, first introduced in 1930. Like horse racing, it is popular to bet on the greyhound races as a form of parimutuel gambling.

In common with many other sports, greyhound racing enjoyed its highest attendances just after the Second World War—for example, there were 34 million paying spectators in 1946. The sport experienced a decline from the early 1960s, when the 1960 Betting and Gaming Act permitted off-course cash betting, although sponsorship, limited television coverage, and the later abolition of on-course betting tax have partially offset this decline.
After the dogs are no longer able to race (generally, a greyhound's career will end between the ages of four and six), or as soon as they no longer consistently place in the top four, the dogs' race career ends. The best dogs are kept for breeding purposes. There are both industry-associated adoption groups and rescue groups that work to obtain retired racing greyhounds and place them as pets. In the United Kingdom, according to the BBC, one in four retired greyhounds finds a home as a pet. In the United States, prior to the formation of adoption groups, over 20,000 retired greyhounds a year were euthanized; recent estimates still number in the thousands, with about 90% of National Greyhound Association-registered animals either being adopted, or returned for breeding purposes (according to the industry numbers upwards of 2000 dogs are still killed annually in the US while anti-racing groups estimating the figure at closer to 12,000.). Other greyhounds are either sold to research labs, or sent to foreign racetracks, sometimes in developing countries.

Several organizations, such as British Greyhounds Retired Database, Adopt-a-Greyhound and Greyhound Pets of America, and the retired greyhound trust try to ensure that as many of the dogs as possible are adopted. Some of these groups also advocate better treatment of the dogs while at the track and/or the end of racing for profit. In recent years the racing industry has made significant progress in establishing programs for the adoption of retired racers. In addition to actively cooperating with private adoption groups throughout the country, many race tracks have established their own adoption programs at various tracks.

In recent years, several state governments in the United States have passed legislation to improve the treatment of racing dogs in their jurisdiction. During the 1990s seven states banned live greyhound racing, though racing has never been banned in a state that has had active racing.

In venues where greyhound racing does not involve gambling, the dogs are almost invariably pets and are, therefore, generally well treated.