A coat of arms is a unique heraldic design on a shield or escutcheon or on a surcoat or tabard used to cover and protect armour and to identify the wearer. Thus the term is often stated as "coat-armour", because it was anciently displayed on the front of a coat of cloth. The coat of arms on an escutcheon forms the central element of the full heraldic achievement which consists of shield, supporters, crest and motto. The design is a symbol unique to an individual person, and to his family, corporation, or state. Such displays are commonly called armorial bearings, armorial devices, heraldic devices, or simply armorials or arms.

Historically, armorial bearings were first used by feudal lords and knights in the mid-12th century on battlefields as a way to identify allied from enemy soldiers. As the uses for heraldic designs expanded, other social classes who never would march in battle began to assume arms for themselves. Initially, those closest to the lords and knights adopted arms, such as persons employed as squires that would be in common contact with the armorial devices. Then priests and other ecclesiastical dignities adopted coats of arms, usually to be used as seals and other such insignia, and then towns and cities to likewise seal and authenticate documents. Eventually by the mid-13th century, peasants, commoners and burghers were adopting heraldic devices. The widespread assumption of arms led some states to regulate heraldry within their borders. However, in most of continental Europe, citizens freely adopted armorial bearings.