Auxiliary police, also called volunteer police, reserve police, assistant police, civil guards, or special police, are usually the part-time reserves of a regular police force. They may be unpaid volunteers or paid members of the police service with which they are affiliated.

Special police usually describes a police force or unit within a police force whose duties and responsibilities are significantly different from other forces in the same country or from other police in the same force, although there is no consistent international definition. A special constable, in most cases, is not a member of a special police force (SPF); in countries in the Commonwealth of Nations and often elsewhere, a special constable is a voluntary or part-time member of a national or local police force or a person involved in law enforcement who is not a police officer but has some of the powers of a police officer.