A Commissioner is one of various classes of persons who holds an office by virtue of a commission, normally from the head of state.

In the Commonwealth of Nations, a Commissioner is the ceremonial head of one of the Territories of Canada. It is also the title of the chief official of some of the minor overseas territories of the United Kingdom.

A Commissioner is also a diplomatic envoy from one Commonwealth Government to another, stationed outside the capital city, who heads a mission equivalent to a consulate.