Armor, any equipment of various materials, but generally of metal, used to protect a body in combat. The oldest of protective devices is the shield; the earliest body armor was a wide belt to protect the abdomen.

In ancient Egypt (circa 3000 BC) this belt was developed into a wraparound garment extending from armpits to knees, reinforced by quilting, and held up by shoulder straps. In Syria (circa 1400 BC) the national costume, a sleeved shirt, was reinforced with bronze scales and used as armor for charioteers, who with both hands occupied were unable to hold a shield. The scales were sewn onto a fabric backing or were laced together in flexible rows of lamellae. Helmets, in the form of tight-fitting caps of beaten copper, were first used by the Sumerians (c. 3000 BC). Assyrian helmets were conical bronze caps with small earflaps.

Both scale and lamellar armor were taken over by the Scythians and the Greeks. Greek armor was a wraparound of reinforced quilts with wide shoulder flaps; its lower part was a skirt of loose strips, or pteryges. A cuirass, or thorax, of hammered bronze plates realistically embossed to portray the muscles of a naked torso was also worn to protect chest and back. Greek body armor was completed by bronze greaves, that is, a covering for the lower legs, and by a round oxhide shield. Helmets were designed to enclose the entire head; in their perfected form only a Y-shaped opening for eye-slits and for breathing was left.

The cuirass (lorica) worn by Roman soldiers was a modification of Greek armor and existed in three basic versions: lorica squamata, with bronze scales on a leather backing; lorica hamata, made of mail, that is, of interlinked iron rings; and lorica segmentata, constructed of horizontally overlapping iron plates. Roman helmets, of bronze or iron, had movable cheek pieces. The large rectangular Roman shield made greaves superfluous.

Roman technology survived in the armament of the most typical figure of the European Middle Ages, the knight. By the 11th century a knight's armor consisted of a thigh-length shirt of mail (known as a hauberk) with elbow-length sleeves and a conical helmet with nose guard. In the 12th century the mail shirt gained an attached hood (coif), and the sleeves were full length, terminating in mittens. Mail chausses protected the legs. A mail shirt, containing up to 250,000 metal rings, might weigh about 11 kg (about 25 lb). Mail offers resistance to sword cuts, but it can be penetrated by the points of spears or arrows and is too yielding against a heavy blow. A padded undergarment, or acton, and a shield were, therefore, essential as shock breakers.

Bolts released by the improved crossbows introduced in the first quarter of the 14th century were able to penetrate mail with ease. Armor with deflecting surfaces, therefore, became necessary. This was achieved, about 1350, by the development of full plate defenses for arms and legs and body armor made of small plates riveted inside the surcoat, known as a coat of plates or brigandine. The loose-fitting mail shirt was slipped on over the head, but the coat of plates had to be tight-fitting and opened in front. The fighting position was with the left, shield-protected side toward the enemy; to deflect spear points and sword blades, therefore, the coat of plates had to be buckled with its left side overlapping the right. (For this reason, men's jackets are still buttoned left over right.)

The fully articulated plate armor developed in the first half of the 15th century is called Gothic, because of its emphasis on vertical lines and its spiky silhouette reminiscent of Gothic architecture. About 1500 the style changed, with the more rounded shapes characteristic of Renaissance style dominant; a variant favored in Germany for its additional strength (the so-called Maximilian armor, after the emperor Maximilian I) had fluted surfaces, like corrugated iron.

Armor-making centers were located in Milan and Brescia, Italy; Augsburg, Nürnberg, and Landshut, Germany; Innsbruck, Austria; Paris and Tours, France; and Antwerp and Brussel, Belgium. Metal armor was expensive and thus restricted to the wealthy warrior. Some reigning princes (notably in Bourgogne, France, and England) had court armories of their own, mainly for the manufacture of elaborate suits of armor to be used as diplomatic presents. Armor as a status symbol was enhanced by decoration. Surface ornamentation by etching and gilding did not lower its defensive value (gilding was actually a rust-proofing device), but highly embossed plates defeated the purpose of armor as a deflecting surface. The embossed parade armors popular in the 16th century were strictly body jewelry, made by specialist artisans.

Best known among non-European armor is that of the Japanese samurai; these feudal warriors wore wraparound lamellar armor with shoulder flaps and skirt akin to the ancient Greek patterns. Such protected costumes were worn in Japan until 1876, and in Tibet similar armor was worn into the 20th century. Nonmetallic versions of bone or wood lamellae were worn by the Chukchi in Kamchatka, the Inuit (Eskimo) in Alaska, and the Iroquois in New York State (at the time of European contact). Excavations in China have yielded clay statues of warriors, dating from the 3rd century BC, represented as wearing lamellar armor of a pattern similar to the Roman lorica segmentata. In India, Persia, and Turkey, armor consisted primarily of mail, sometimes reinforced with small rectangular plates. Helmets were pointed, with movable cheek pieces and a neck guard (in Turkey), or with a camail, a hanging curtainlike piece of mail to protect neck and chest (in Persia).

In Mexico, at the time of the Spanish conquest, quilted jackets were worn by the Aztecs and other Native Americans; these garments were so efficient against flint-tipped arrows that the invading Spaniards soon adopted them for their own use. Similar quilted armor and helmets reinforced with basketwork were the equipment of the Inca warriors of Peru. The Plains peoples of North America had breastplates made of bone tubes arranged in rows, but most tribes both in North and South America wore little body armor. Even the armored Iroquois used such gear not for offensive warfare but in combat waged in the defense of their villages.

While a knight in full armor was almost invulnerable to pointed or edged weapons, the impact of a soft lead bullet could break an armor plate. Thus, as guns and gunpowder replaced older weaponry, armor began to be modified. Thicker plates afforded needed protection against bullets but greatly increased the weight of the armor. For this reason, by the late 16th century, overall protection was sacrificed in favor of partial armor; by the mid-17th century only the cuirass and helmet survived. In the 18th and 19th centuries cuirasses were still used—as protection against sword cuts.

During World War I a soldier's body was effectively protected inside a trench or foxhole, but steel helmets were required as protection against shrapnel; the first such helmets were introduced by the German army in 1915. Armor in the form of steel helmets and flak jackets is still used in modern warfare. Aside from military use, armor in the form of visored helmets, bulletproof vests, and shields is indispensable in modern times for special police work. Armor has its place too in more peaceful, though hazardous, occupations and recreations. Hard hats (a form of helmet) are worn by miners and construction workers, and—sometimes with elaborate additional protection devices—in many contact sports.