When wearing armour in battle, it was difficult to see who was who. Uniforms were no use, because people tended to change sides from time to time.

From about the early 12th century, combatants would wear symbols on badges, shields or flags, or on cloth worn outside the armour. It was literally a coat, with the symbols or 'arms' painted on: thus a 'coat of arms'. The symbols were simple, bold and colourful to make them easily recognisable.

The 'coat of arms' were passed on from generation to generation (usually in the male line), so they came to represent families rather than individuals.

Official messengers, known as heralds, were used to pass messages between the armies and their kings or princes. They obviously had to know which symbols represented which families so the designs were recorded in books called 'armorials'. Armorials contained illustrations with a description including colours, in a language based on an ancient form of French, the language used by most of the ruling classes since the 1066 invasion of William.

By about 1200 a protocol prevented anyone from using a coat of arms already used by someone else. This was taken to be 'common law' by around 1400. From then, a coat of arms could only be used if it was granted by the king and this was regulated by the heralds. This is essentially unchanged in Britain now, where coats of Arms can only be granted by Royal Warrant.