An auxiliary cop, also known as an auxiliary police officer, is a part-time reserve of a regular police force. They may be unpaid volunteers or paid members of the police service with which they are affiliated. Auxiliary police officers are primarily tasked with supporting and augmenting the police, but this may also extend to established emergency services such as the fire department, emergency medical services, border patrol, and coast guard. Duties commonly assigned to auxiliaries include community policing, neighborhood watch, traffic policing, civil defense, and riot control.

Auxiliary police officers are not sworn police officers, are not vested with arrest powers, and are not authorized to carry firearms. They serve as non-compensated volunteers in non-enforcement capacities, supportive of the police department and consistent with their demonstrated level of expertise and the needs of the department as determined by the police commissioner. However, in some cases, auxiliary officers may have law-enforcement powers equivalent to those of paid officers.

The requirements to become an auxiliary police officer vary by jurisdiction, but generally, citizens must meet minimum requirements and pass the auxiliary police training program. The training standards for auxiliary police officers are graduated and based upon their level of responsibility as identified by the Auxiliary Police Task Force. Auxiliary police officers are often called upon to assist in large-scale searches for missing persons, to provide crowd control at large-scale events, and often accompany regular force police officers on daily patrols.