King of Arms is the title given to a kingdom's chief heralds.

In the United Kingdom today, there is one king of arms for Scotland, Lord Lyon King of Arms, and three at the College of Arms in London (with jurisdiction over England, Wales, and Northern Ireland): Garter Principal King of Arms; Clarenceaux King of Arms (with jurisdiction south of the river Trent); and Norroy and Ulster King of Arms (with jurisdiction north of the Trent and in Northern Ireland).

The English kings of arms assigned coronets of oak leaves inscribed miserere mei, deus (Latin: "have mercy on me, God"); a new coronet (modeled on the crown among the Honours of Scotland) has recently been made for the Lord Lyon. However, these coronets are only worn at coronations; for most state occasions, kings-of-arms wear the same sort of beret-like hat which other heralds wear.