Commissioner is a senior rank used in many police forces and may be rendered Police Commissioner or Commissioner of Police. In some organizations, the commissioner is a political appointee, and may or may not actually be a professional police officer. In these circumstances, there is often a professional chief of police in charge of day-to-day operations. Usually, however, the commissioner is the professional head of the organization.^{[citation needed]}

In police services in the Commonwealth and the USA, the title of commissioner typically designates the head of an entire police force. In some countries, such as in many Latin American countries and in France, the title of commissioner is more junior and instead refers to the head of a single police station (similar to Chief Superintendents in the Commonwealth).

In most states and territories of Australia, the highest ranking Police Officer is a commissioner, aside from Victoria, which during the Gold Rush had a Commissioner for both the Metropolitan Area and the Goldfields. The rank of Chief Commissioner was introduced to provide a single head of the Police and, despite the disappearance of the rank of Commissioner, nowadays the second highest rank is Deputy Commissioner, the title of Chief Commissioner for the head of Victoria Police has remained since.

Assistant commissioner is a rank used in many police forces across the globe. It is also a rank used in revenue administrations (Land, Customs, Inland etc.) in many countries.

In all Australian police forces, excepting the New South Wales Police Force where it is junior to the rank of senior assistant commissioner, assistant commissioner is the rank below deputy commissioner but senior to the rank of commander (South Australia Police, Victoria Police), senior to the rank of superintendent (Western Australia Police) and senior to the rank of chief superintendent (Queensland Police Service, New South Wales Police Force). In all services, the insignia consists of crossed and wreathed tipstaves; as a rank, it is roughly equivalent to that of a brigadier or major-general in the army.

The rank of assistant commissioner is used by one police agency:

Hong Kong Police Force have two ranks for assistant deputy commissioner:

In that country, senior officers of the rank of assistant superintendent/assistant commissioner of police or above may belong to the national Indian Police Service or state police services, whereas Indian inspectors and constables belong to the individual provincial police forces.