A greave (from 12th century French greve "shin", of uncertain origin) is a piece of armour that protects the leg.

Often in matched pairs (a pair of greaves), greaves may be constructed of materials ranging from padded cloth to steel plate. Some designs protect only the lower leg (a half-greave) or extend upwards to protect the thigh. Greaves can also be called platelegs.

Greaves are most commonly found in the armor of heavy infantry, usually from ancient times. One example of infantry using greaves are ancient Greek Hoplites. Also, later Roman Legion infantrymen wore greaves. The Roman Centurions wore altered greaves from the standard Roman uniform.