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.

An officer of arms is a person appointed by a sovereign or state with authority to perform one or more of the following functions:to control and initiate armorial matters; to arrange and participate in ceremonies of state; to conserve and interpret heraldic and genealogical records.