Harness racing has been around in some form since the beginning of recorded history, and probably before then. The ancient Greek Olympics featured both mounted horseracing and chariot races, and ancient Rome's Circus Maximus ran two dozen races a day, complete with bookmakers, changing odds, and highly sought-after “inside” tips.

Today, there are more harness racing tracks, and more harness races, per year than there are Thoroughbred tracks and races in the United States. Harness racing also is popular in other countries, including most of Europe, Canada, Australia, and New Zealand. In Spain, harness races are held on beaches, while in Switzerland horses race along snow-covered tracks in the winter. In many countries, harness races are held on grass courses. Most U.S tracks have dirt or clay surfaces.

Harness races don't begin from a dead stop as mounted races do. In a harness race, the horses are lined up on the track before a mobile “gate” attached to a car or truck. The car or truck drives around the track, or a portion of it, allowing the horses to get up to speed. When the gate passes the starting line, the car or truck accelerates and moves out of the way so the race can begin.

As harness racing grew in popularity, breeders established the standard-bred horse, with specific attributes suited for harness racing — endurance, temperament, and anatomy. The name “standardbred” stems from the practice of basing harness racing speed records on a standard distance of one mile.

Today's standardbreds all trace their lineage back to Imported Messenger, an English Thoroughbred brought to the United States in the 1780s and bred to both Thoroughbred and mixed-breed mares. One of Messenger's great-grandsons, Hambletonian, greatly influenced the standardbred bloodline. Hambletonian sired four prominent racers that, in their turn, produced lines that included Lou Dillon, the first trotter to run a mile in two minutes.

Standardbred horses are classified as either trotters or pacers. A trotter moves his or her legs diagonally, balancing the weight on the front right and hind left, or the front left and hind right, while running. Pacers, on the other hand, move laterally, with the front and hind legs on the right hitting the ground together, followed by the left front and hind legs.

Young Standardbreds go through a series of training steps while learning to race. In the first stage, the trainer walks behind the horse and teaches it to respond to movements of the reins and harness. In the second stage, the horse learns to pull a training cart, which is usually heavier than the sulky that the horse will pull during a race. All racing horses also go through regular training exercises to develop their speed and skills and to maintain their condition as their careers progress.