In the United States, the Triple Crown of Thoroughbred Racing, commonly known as the Triple Crown, is a series of horse races for three-year-old Thoroughbreds, consisting of the Kentucky Derby, Preakness Stakes, and Belmont Stakes. The three races were inaugurated in different years, the last being the Kentucky Derby in 1875. The Triple Crown Trophy, commissioned in 1950 but awarded to all previous winners as well as those after 1950, is awarded to a horse who wins all three races and is thereafter designated as a Triple Crown winner. The races are traditionally run in May and early June of each year, although global events have resulted in schedule adjustments, such as in 1945 and 2020.

The first winner of all three Triple Crown races was Sir Barton in 1919. Some journalists began using the term Triple Crown to refer to the three races as early as 1923, but it was not until Gallant Fox won the three events in 1930 that Charles Hatton of the Daily Racing Form put the term to common use.

Only 13 horses have ever won the Triple Crown: Sir Barton (1919), Gallant Fox (1930), Omaha (1935), War Admiral (1937), Whirlaway (1941), Count Fleet (1943), Assault (1946), Citation (1948), Secretariat (1973), Seattle Slew (1977), Affirmed (1978), American Pharoah (2015), and Justify (2018). As of 2024, American Pharoah and Justify are the only living Triple Crown winners.

James E. "Sunny Jim" Fitzsimmons was the first trainer to win the Triple Crown more than once; he trained both Gallant Fox and Omaha for the Belair Stud. Gallant Fox and Omaha are also the only father-son pair to each win the Triple Crown. Bob Baffert became the second trainer to win the Triple Crown more than once, training American Pharoah and Justify. Belair Stud and Calumet Farm are tied as owners with the most Triple Crown victories with two apiece; Calumet's winners were Whirlaway and Citation. Eddie Arcaro rode both of Calumet's Triple Crown champions and is the only jockey to win more than one Triple Crown. Willie Simms is the only African-American jockey to win all three races that would compose the triple crown. During the 1898 Preakness Stakes he rode a different horse, Sly Fox and won the race.

Secretariat holds the stakes record time for each of the three races. His time of 2:24 for 1+1⁄2 miles in the 1973 Belmont Stakes also set a world record that still stands.