Clarenceux King of Arms, historically often spelled Clarencieux, is an officer of arms at the College of Arms in London. Clarenceux is the senior of the two provincial kings of arms and his jurisdiction is that part of England south of the River Trent. The office almost certainly existed in 1420, and there is a fair degree of probability that there was a Claroncell rex heraldus armorum in 1334. There are also some early references to the southern part of England being termed Surroy, but there is not firm evidence that there was ever a king of arms so called. The title of Clarenceux is supposedly derived from either the Honour of the Clare earls of Gloucester, or from the Dukedom of Clarence (1362). With minor variations, the arms of Clarenceux have, from the late fifteenth century, been blazoned as Argent a Cross on a Chief Gules a Lion passant guardant crowned with an open Crown Or.

King of arms is the senior rank of an officer of arms. In many heraldic traditions, only a king of arms has the authority to grant armorial bearings and sometimes certify genealogies and noble titles. In other traditions, the power has been delegated to other officers of similar rank.