Commissioner is in principle the title given to a member of a commission, in the sense of a mandate, whether individually or shared, notably as member of a collegial commission.

In practice the title of commissioner has evolved to include a variety of senior officials, often sitting on a specific commission. In particular, commissioner frequently refers to senior police or government officials. A High Commissioner is equivalent to an ambassador, between Commonwealth states sharing the same Monarch as head of state.

The title is also sometimes given to senior officials in the private sector, for instance many North American sports leagues.

Domestic public official

A Commissioner within a modern state generally holds his office by virtue of a commission from the head of state or a council of elected representatives (or appointed by non-elected officials in the case of dictatorships).

Imperial China

Senior Public Servants, Commissioners and other high ranking bureaucrats referred to collectively as Mandarins.

===Canadian territories

Police

main: Police commissioner

In police services in the Commonwealth and USA, the title of commissioner typically designates the head of an entire police force(e.g., the New York City Police Department, or the California Highway Patrol). In some countries, such as in many Latin American countries and in France, the title of commissioner rather refers to the head of a single police station.

Scotland

Prior to the Acts of Union 1707, an elected member of the Estates (parliament) of Scotland held the office of Commissioner, representing a constituency (the equivalent of a Member of Parliament in the contemporaneous Parliament of England). There were Burgh Commissioners and Shire or Stewartry Commissioners.

United States

In many U.S. states, the legislative and executive decision-making bodies of counties are called the board of commissioners or county commission. In Minnesota, Alaska, New York and Tennessee, the heads of statewide cabinet-level departments are called "commissioners". In California, commissioners are subordinate judicial officers.

British and Commonwealth overseas possessions

The title of Commissioner, as such, was used by the (gubernatorial) chief British official in:

• British Central Africa
• Territories of Zambesia and Rhodesia, administered under charter by the British South Africa Company
• the Oil Rivers Protectorate (from 5 June 1885 under a consul-general; soon renamed Niger Coast Protectorate), from 3 August 1891 till 1 January 1900 when it became the Protectorate of Southern Nigeria, hence under a High Commissioner
• the Caribbean Turks and Caicos Islands, 1874 - 4 July 1959, as a dependency under the Governor of Jamaica colony
• the Weihaiwei concession territory (held from China) from 1902 to 1938
• Kamaran Island, in June 1915 taken from the Ottoman Empire and subordinated to the Aden Settlement, but not incorporated, till on 30 November 1967 it became part of the newly independent People's Republic of South Yemen.
• the UN trust territory of British Cameroons, only two incumbents, from 1 October 1954 (the only Special Resident succeeding himself till 1956) to 1 October 1961 when Southern British Cameroons is incorporated into the independent Republic of Cameroon (former French mandate of Cameroun), after the northern part united with Nigeria on 1 June 1961