Trakehner (/trəˈkeɪnər/) is a warmblood breed of horse, originally developed at the East Prussian state stud farm in the town of Trakehnen from which the breed takes its name. The state stud [de] was established in 1731 and operated until 1944, when the fighting of World War II led to the annexing of East Prussia by Russia, and the town containing the stud renamed as Yasnaya Polyana.

The Trakehner typically stands between 15.2 and 17 hands (62 and 68 inches, 157 and 173 cm). They can be any color, with bay, gray, chestnut and black being the most common, though the breed also includes few roan and tobiano pinto horses. It is considered to be the lightest and most refined of the warmbloods, due to its closed stud book which allows entry of only Trakehner, as well as few selected Thoroughbred, Anglo-Arabian, Shagya and Arabian bloodlines.

Owing to its Thoroughbred ancestry, the Trakehner is of rectangular build, with a long sloping shoulder, good hindquarters, short cannons, and a medium-long, crested and well-set neck. The head is often finely chiseled, narrow at the muzzle, with a broad forehead. It is known for its "floating trot" – full of impulsion and suspension. The Trakehner possesses a strong, medium-length back and powerful hindquarters.

Trakehners are athletic and trainable, with good endurance, while some are more spirited than horses of other warmblood breeds. Trakehners breed true to type, due to the purity of the bloodlines, making it valuable for upgrading other warmbloods.

Old Prussians and other Baltic people such as the Lithuanians were noted for their hardy horses and cavalry during the early Middle Ages. During their conquest of Old Prussians in the 13th century Prussian crusade, the conquering Teutonic Knights named the Old Prussian horse a Schwaikenpferd, a small primitive horse. Beginning in the 14th century, knights used it to breed their military horses, and descendants of the Schwaikenpferd were later used by Masovian and Ostsiedlung farmers for light utility work. During the 16th and 17th centuries, the people of Ducal Prussia, Brandenburg, and Royal Prussia used a wide variety of horses from the Polish–Lithuanian Commonwealth, Crimean Tatars, Ottoman Turkey, Wallachia, Moldavia and Transylvania, Holy Roman Empire for their cavalry and stud horses, crossed on local animals.

In 1732 King Frederick William I of Prussia used these horses and other imports to establish the Trakehnen Stud at the East Prussian town Trakehnen (now Yasnaya Polyana, Russia). Soldiers cleared the forest at the River Pissa between Stallupönen and Gumbinnen. In 1739 the king gave it to crown prince Frederick II of Prussia, who often sold stallions to make money. After his death in 1786 it became state property, named Königlich Preußisches Hauptgestüt Trakehnen.

Between 1817 and 1837 the stud added Arabian, Thoroughbred, and Hanoverian horse blood to their stock. One especially influential Thoroughbred was Perfectionist, by Persimmon, who won The Derby and the St Leger in 1896. He was to be the sire of the great Trakehner stallion Tempelhüter, and most modern Trakehners can be traced to these two stallions. The Arabian blood was added to offset possible flaws of the Thoroughbred.

East Prussian farmers were encouraged to bring their mares, by then known for their hardiness and quality, to Trakehnen's stallions. This enabled the rapid transformation of the breed into much sought-after army remounts: sure-footed, intelligent and athletic. By 1918 60,000 mares per year were bred to East Prussian stallions.