List of leading Thoroughbred racehorses

The list of leading Thoroughbred racehorses contains the names of undefeated racehorses and other horses which had an outstanding race record in specific categories. Note though that many champions do not appear on the list as an unexpected defeat may be caused by many factors such as injury, illness, going, racing tactics and differences in weight carried, the latter being particularly significant in North America and Australia where handicaps are common even at the highest level of racing.

A good, consistent racehorse requires ability to defeat its rivals, especially speed and stamina in varying degrees depending on the type of race. It is common to compare racehorses on multiple factors such as their overall race record, the quality of the horses they beat and the brilliance of their wins. Winning all three at the Triple Crown races is a rare achievement and is considered one of the greatest accomplishments for a Thoroughbred racehorse. Comparison of raw times is generally unreliable between horses of different eras or even in different countries. Time variations may occur as a result of racing surface, track conditions, the pace at which the race is run, etc. Timeform ratings, introduced in 1948, and Beyer Speed Figures, introduced in the United States in 1992, are relatively recent attempts to compensate for such variables. Thoroughbred Winning Brew holds the Guinness world record for the fastest speed for a racehorse, at 70.76 km/h (43.97 mph) over two furlongs, although Quarter Horses attain higher speeds over shorter distances than Thoroughbreds. Looking at average speeds for longer distances may be misleading as many races are run with a slow initial pace followed by a sprint in the stretch drive.

The two main forms of Thoroughbred horseracing are flat racing and hurdle or steeplechase (jumping) races over obstacles. Jumpers tend to be older than their flat racing counterparts and can have much longer careers, making it possible to earn a large number of wins. For example, champion hurdler Hurricane Fly holds a world record for winning 22 Grade One races over his ten-year career.

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