Auxiliary police are usually the part-time reserves of a regular police force. They may be armed or unarmed. They may be unpaid volunteers or paid members of the police service with which they are affiliated. In most jurisdictions, Auxiliary Police officers are empowered to make arrests for crimes that occur in their presence.

In Canada, many police forces utilize the services of auxiliary constables. Under various provincial policing legislations and the Royal Canadian Mounted Police Act, the role of auxiliary constable is to assist regular, or sworn, police constables in the execution of their duties, as well as to provide assistance in community policing.

Auxiliary constables in Canada wear uniforms similar to regular force constables. However, most wear the word "auxiliary" on a rocker panel under the force's crest on each arm, and in some cases, wear a red and black checkered head band on their service caps to distinguish them from full-time police. Also, auxiliary constables are usually unarmed, but are trained in firearms. They may, depending on legislation and policies, carry a baton and handcuffs while on duty.

A police officer (also known as a policeman or policewoman, and constable in some forces, particularly in the United Kingdom and other Commonwealth nations) is a warranted employee of a police force. In the United States, "officer" is the formal name of the lowest police rank; in many other countries "officer" is a generic term not specifying a particular rank, and the lowest rank is often "constable". Police officers are generally charged with the apprehension of criminals and the prevention and detection of crime, and the maintenance of public order. Police officers may be sworn to an oath, and have the power to arrest people and detain them for a limited time, along with other duties and powers.

Some police officers may also be trained in special duties, such as counter-terrorism, surveillance, child protection, VIP protection, and investigation techniques into major crime, including fraud, rape, murder and drug trafficking.

Responsibilities of a police officer are varied, and may differ greatly from within one political context to another. Typical duties relate to keeping the peace, law enforcement, protection of people and property, and the investigation of crimes. Officers are expected to respond to a variety of situations that may arise while they are on duty. Rules and guidelines dictate how an officer should behave within the community, and in many contexts restrictions are placed on what the uniformed officer wears. In some countries, rules and procedures dictate that a police officer is obliged to intervene in a criminal incident, even if they are off-duty. Police officers in nearly all countries retain their lawful powers, while off duty.