The stirrup is a ring with a flat bottom, usually hung from each side of a saddle to create a footrest for the rider on a horse or, much less often, another animal. It greatly increases the rider's ability to control the horse, making this animal a useful tool in communication, transportation and warfare. As a result it is considered one of the basic tools used to create and spread modern civilization. Some even argue it is as important as the wheel or printing press.

The stirrup was invented surprisingly late in history, considering that horses were used for bareback riding and to pull carts or war chariots since at least 10,000 B.C. The stirrup was apparently invented in China in the first few centuries A.D., and was spread throughout Eurasia by the great horsemen of the central Asia steppes, such as the Mongol empire. Stirrups were not widely used in Europe until the time of Charlemagne.

Stirrup is an informal term for the stapes bone of the ear.