Police forces are government organizations charged with the responsibility of taking care of law and order, and safeguarding the life and interests of the general public from harm. The term "police" was coined originally in France in the 18th century. The police are also often known as a constabulary. This term was derived from constables, who were an early form of police officers. A police officer only refers to those people who have been sworn in as law enforcement officers by way of oath. It does not include civilian support staff that may be uniformed but have certain restricted enforcement powers.

In the United States, policing and law enforcement form a single entity known as the Criminal Justice System, the others being the judiciary and corrections. Theoretically, each arm is independent in function and objectives from the others, although the judicial courts have legal oversight of both. Along with maintaining law and order and other service functions, the purpose of policing also refers to the investigation of suspected criminal activity. Referring the results of such investigations and of suspected criminals to the courts also forms an important function. Duty of a police officer includes protection of life and property. It also includes prevention of crime and detection and arrest of criminals. Apart from this, they are also required to enforce all laws, decrees and provisions of the administrative code over which the police department has jurisdiction.

In the United States, there are compound levels of policing and law enforcement services. This refers to the federal police, state police (often known as state troopers or highway patrol officers) and county police (known as sheriffs, constables, metropolitan police, and some county police agencies). Along with this there also include special-purpose district police (parks, schools, housing, transit, etc), and local police. There are roughly 18,000 independent police agencies.