Armour (or armor) is protective covering, most commonly manufactured from metals, to prevent damage from being inflicted to an individual or a vehicle through use of direct contact weapons or projectiles, usually during combat.

While early armour tended to be worn as clothing intended to defend its wearer during combat between armed forces, armour has been used throughout recorded history, manufactured from a variety of materials, non-metallic and metallic. For much of military history the manufacture of metal armour in Europe has dominated the technology and employment of armour. Its production has been influential in the evolving industrial revolution, and influenced commercial development of metallurgy and engineering.

Armour production was a cause of the development of many important technologies of the Ancient World, including wood lamination, mining, metal refining, vehicle manufacture (chariot), leather processing, and later decorative metal working.

Armour was commonly used to protect only soldiers, foot and mounted. Starting with the rudimentary leather protection, the personal armour evolved to mail and full plated suit of armour. Armour was the single most influential factor in the development of firearms that revolutionised warfare, and has returned in the shape of armoured fighting vehicles in the attempt to enable ground troops to breach field defences unscathed. Sailors and pilots have also benefited from use of armour, with armoured warships dominating naval warfare until the building of the aircraft carriers.

War animals such as elephants and war horses, have also benefited from armour, the application for the later called barding. Armour has also been produced for hunting dogs that hunt dangerous game, such as boars.

First modern production technology for armour plating was used by the navies in construction of the Ironclad warships, and reaching its pinnacle of development with the battleship. It was the naval engineers that also constructed the first World War I "tanks" giving rise to armoured fighting vehicles protected by vehicle armour.

In modern ground forces' usage, the meaning of armour has expanded to include the role of troops in combat. After the evolution of armoured warfare, heavily armoured military forces are organised using armoured infantry, mounted in armoured fighting vehicles and replacing light infantry in many situations. In modern armoured warfare, armoured units equipped with tanks and infantry fighting vehicles serve the historic role of both the battle cavalry, light cavalry and dragoons, and belong to the armoured branch in a national army's organisation (sometimes, the armoured corps).

Air forces also sometimes employ armour. Aerial armour has been used, notably, in protecting the pilots during the Second World War, and in designing heavily armoured aircraft that would be expected to suffer more than usual damage from ground fire.