A stirrup is a light frame or ring that holds the foot of a rider, attached to the saddle by a strap, often called a stirrup leather. Stirrups are usually paired and are used to aid in mounting and as a support while using a riding animal (usually a horse or other equine, such as a mule). They greatly increase the rider's ability to stay in the saddle and control the mount, increasing the animal's usefulness to humans in areas such as communication, transportation, and warfare.

In antiquity, the earliest foot supports consisted of riders placing their feet under a girth or using a simple toe loop appearing in India by the 2nd century BC. Later, a single stirrup was used as a mounting aid, and paired stirrups appeared after the invention of the treed saddle. The stirrup was invented in China in the first few centuries AD and spread westward through the nomadic peoples of Central Eurasia. The use of paired stirrups first appeared in the Chinese Jin dynasty during the 4th century, was in common use throughout China by the 5th century, and spread across Eurasia to Europe by the 7th or 8th century. Some argue that the stirrup was one of the basic tools used to create and spread modern civilization, possibly as important as the wheel or printing press.