The Standardbred is an American horse breed best known for its ability in harness racing where they compete at either a trot or pace.

Developed in North America, the Standardbred is recognized worldwide, and the breed can trace its bloodlines to 18th-century England.

Standardbreds are generally well-muscled and similar to, but a bit heavier than, a Thoroughbred, with a large head often with a Roman nose profile, straight neck, sloping shoulder, defined withers, a deep girth, strong bone (legs) and hard feet.

[5][6] The ability to pace is linked to a single-point mutation in gene DMRT3, which is expressed in the I6 subdivision of spinal cord neurons; this area is responsible for coordinating the locomotor network controlling limb movements.

The point mutation causes early termination of the gene by coding for a stop codon, thus altering the function of this transcription factor.

[10] OC/OCD is a moderate to highly heritable condition in Standardbreds and similar breeds, and genetic risk factors have been identified.

[13] Hambletonian 10 was out of a dam with Norfolk Trotter breeding, and the mare and foal were purchased by William Rysdyk, a farm hand from New York state, who successfully raced the colt as a three-year-old against other horses.

[14] The name arose due to the "standard" required of breeding stock, to be able to trot or pace a mile within a certain time limit.

[19] Today, many Standardbreds are faster than this original standard,[20] with several pacing the mile within 1 min, 50 sec, and trotters only a few seconds slower than pacers.

[6] In 2009, in an effort to reduce the loss of genetic diversity within the breed, the United States Trotting Association capped the studbook for all new sires to 140 mares per year.

By purchasing ex-racehorses, the Amish don't need to have breeding programs or raise young horses—there is a ready supply of mature and trained horses.