Historically, cavalry are soldiers or warriors who fight mounted on horseback. Until the 20th century cavalry were the most mobile of the combat arms, operating as light cavalry in the roles of reconnaissance, screening, and skirmishing in many armies, or as heavy cavalry for decisive shock attacks in other armies. An individual soldier in the cavalry is known by a number of designations depending on era and tactics, such as a cavalryman, horseman, trooper, cataphract, knight, drabant, hussar, uhlan, mamluk, cuirassier, lancer, dragoon, or horse archer. The designation of cavalry was not usually given to any military forces that used other animals for mounts, such as camels or elephants. Infantry who moved on horseback, but dismounted to fight on foot, were known in the early 17th to the early 18th century as dragoons, a class of mounted infantry which in most armies later evolved into standard cavalry while retaining their historic designation.

The first evidence of horses in warfare dates from Eurasia between 4000 and 3000 BC. A Sumerian illustration of warfare from 2500 BC depicts some type of equine pulling wagons. By 1600 BC, improved harness and chariot designs made chariot warfare common throughout the Ancient Near East, and the earliest written training manual for war horses was a guide for training chariot horses written about 1350 BC. As formal cavalry tactics replaced the chariot, so did new training methods, and by 360 BC, the Greek cavalry officer Xenophon had written an extensive treatise on horsemanship. The effectiveness of horses in battle was also revolutionized by improvements in technology, such as the invention of the saddle, the stirrup, and the horse collar.