Commissioner is in principle the title given to a member of a commission or to an individual who has been given a commission (official charge or authority to do something, the noun's second meaning).

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, originally between the United Kingdom and the Dominions sharing the British Monarch as head of state and now between all Commonwealth states whether Commonwealth Realms, Commonwealth Republics or Commonwealth states having their own monarchs. 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

!-- This section is linked from Provinces and territories of Canada --> A Commissioner is the formal head of one of the territories of Canada (i.e. those areas within the country without the constitutional status of a province). Unlike the Governor General or a Lieutenant Governor, who are representatives of the Queen of Canada, Commissioners are not vice-regal representatives, although they too perform duties akin to such including reading the Speech from the Throne at the opening of the territorial Legislature. They are appointed by the federal government as delegates of cabinet. Under the federal statutes[1][2][3] governing the territories, the Commissioners act in accordance with written instructions from cabinet or the minister responsible (currently the Minister of Indian Affairs and Northern Development). While commissioners used to have a direct day-to-day role in administration and government and chaired the Executive Council of the territory, today they are under instruction to act more like provincial Lieutenant-Governors, as territorial assemblies have taken on more responsibility.

A Commissioner of a Territory is eligible to present the Vice-Regal Commendation to any Canadian Forces Members as any Lieutenant-Governors for long-term or outstanding service to the Office of a Lieutenant-Governor or Commissioner.[4]