Police are agents or agencies empowered to enforce the law and to effect public and social order through the legitimate use of force. The term is most commonly associated with police departments of a state that are authorized to exercise the police power of that state within a defined legal or territorial area of responsibility. The word comes via French from the Latin politia ("civil administration"), which itself derives from the Ancient Greek πόλις, for polis ("city"). Alternative names for police force include constabulary, gendarmerie, police department, police service, or law enforcement agency, and members can be police officers, constables, troopers, sheriffs, rangers, or peace officers. Russian police and police of the Soviet-era Eastern Europe is (or was) called militsiya.
In England and Wales, each police force or service is overseen by a police authority.

History
In Ancient Greece, publicly-owned slaves were used by magistrates as police. In Athens, a group of 300 Scythian slaves was used to guard public meetings to keep order and for crowd control, and also assisted with dealing with criminals, manhandling prisoners, and making arrests. Other duties associated with modern policing, such as investigating crimes, was left to the citizens themselves. The Roman Empire had a reasonably effective law enforcement system until the decline of the empire. When under the reign of Augustus the capital had grown to almost one million inhabitants, he created 14 wards, which were protected by seven squads of 1,000 men called "Vigiles," who guarded against fires and served as nightwatchmen. If necessary, they might have called the Praetorian Guard for assistance. Beginning in the 5th century, policing became a function of clan chiefs and heads of state.
The Anglo-Saxon system of maintaining public order was a private system of tithings, since the Norman conquest led by a constable, which was based on a social obligation for the good conduct of the others; more common was that local lords and nobles were responsible to maintain order in their lands, and often appointed a constable, sometimes unpaid, to enforce the law.

Pre-modern Europe
In Western culture, the contemporary concept of a police paid by the government was developed by French legal scholars and practitioners in the 17th century and early 18th century, notably with Nicolas Delamare's Traité de la Police ("Treatise on the Police", published between 1705 and 1738). The German Polizeiwissenschaft (Science of Police) was also an important theoretical formulation of police.
The first police force in the modern sense was created by the government of King Louis XIV in 1667 to police the city of Paris, then the largest city of Europe and considered the most dangerous European city. The royal edict, registered by the Parlement of Paris on March 15, 1667 created the office of lieutenant général de police ("lieutenant general of police"), who was to be the head of the new Paris police force, and defined police as the task of "ensuring the peace and quiet of the public and of private individuals, purging the city of what may cause disturbances, procuring abundance, and having each and everyone live according to their station and their duties". This office was held by Gabriel Nicolas de la Reynie, who had 44 commissaires de police (police commissioners) under his authority. In 1709, these commissioners were assisted by inspecteurs de police (police inspectors). The city of Paris was divided into 16 districts policed by the 44 commissaires de police, each assigned to a particular district and assisted in their districts by clerks and a growing bureaucracy. The scheme of the Paris police force was extended to the rest of France by a royal edict of October 1699, resulting in the creation of lieutenants general of police in all large French cities or towns.
As conceptualized by the Polizeiwissenschaft, the police had an economical and social duty ("procuring abundance"). It was in charge of demographics concerns and of empowering the population, which was considered by the mercantilist theory to be the main strength of the state. Thus, its functions largely overreached simple law enforcement activities, and included public health concerns, urban planning (which was important because of the miasma theory of disease; thus, cemeteries were moved out of town, etc.), surveillance of prices, etc. .
Development of modern police was contemporary to the formation of the state, later defined by sociologist Max Weber as detaining "the monopoly on the legitimate use of physical force," primarily exercised by the police and the military. Despite its differences, this definition was not completely alien to the Marxist definition of the state as a "repressive apparatus" guarding the bourgeoisie's interests.

The invention of "police"
After the troubles of the French Revolution the Paris police force was reorganized by Napoléon I on February 17, 1800 as the Prefecture of Police, along with the reorganization of police forces in all French cities with more than 5,000 inhabitants. On March 12, 1829, a government decree created the first uniformed policemen in Paris and all French cities, known as sergents de ville ("city sergeants"), which the Paris Prefecture of Police's website claims were the first uniformed policemen in the world.

Modern police
In most Western police forces, perhaps the most significant division is between preventive ("uniformed") police and detectives. Terminology varies from country to country. Police functions include protecting life and property, enforcing criminal law, criminal investigations, regulating traffic, crowd control, and other public safety duties.

Personnel and organization
Preventive Police, also called Uniform Branch, Uniformed Police, Uniform Division, Administrative Police, Order Police, or Patrol, designates the police which patrol and respond to emergencies and other incidents, as opposed to detective services. As the name "uniformed" suggests, they wear uniforms and perform functions that require an immediate recognition of an officer's legal authority, such as traffic control, stopping and detaining motorists, and more active crime response and prevention. Preventive police almost always make up the bulk of a police service's personnel. In Australia and Britain, patrol personnel are also known as "general duties" officers. Unusually, in Brazil, preventive police are known as Military Police.

Preventive police
Detective Police, also called Criminal Investigation Department (CID), Investigations Police, Judiciary Police / Judicial Police, or Criminal Police, are responsible for investigations and detective work. They typically make up roughly 15% - 25% of a police service's personnel.
Detectives, by contrast to uniform police, typically wear 'business attire' in bureaucratic and investigative functions where a uniformed presence would be either a distraction or intimidating, but a need to establish police authority still exists. "Plainclothes" officers dress in attire consistent with that worn by the general public for purposes of blending in. In some cases, police are assigned to work "undercover", where they conceal their police identity to investigate crimes, such as organized crime or narcotics crime, unsolvable by other means. In some cases this type of policing shares some aspects with espionage.
Despite popular conceptions promoted by movies and television, many US police departments prefer not to maintain officers in non-patrol bureaus and divisions beyond a certain period of time, such as in the detective bureau, and instead maintain policies that limit service in such divisions to a specified period of time, after which officers must transfer out or return to patrol duties. This is done in part based upon the perception that the most important and essential police work is accomplished on patrol in which officers become acquainted with their beats, prevent crime by their presence, respond to crimes in progress, manage crises, and practice their skills. Detectives, by contrast, usually investigate crimes after they have occurred and after patrol officers have responded first to a situation. Investigations often take weeks or months to complete, during which time detectives spend much of their time away from the streets, in interviews and courtrooms, for example. Rotating officers also promotes cross-training in a wider variety of skills, and serves to prevent "cliques" that can contribute to corruption or other unethical behavior.

Detective police
Police may also take on auxiliary administrative duties, such as issuing firearms licenses. The extent that police have these functions varies among countries, with police in France, Germany, and other continental European countries handling such tasks to a greater extent than British counterparts.

Specialized units
Police services commonly include units for investigating crimes committed by the police themselves. These units are typically called Inspectorate-General, or in the USA, "internal affairs". In some countries separate organizations outside the police exist for such purposes, such as the British Police Complaints Authority (now Independent Police Complaints Commission). Likewise, some state and local jurisdictions, for example, Springfield, Illinois have similar outside review organizations. The Police Service of Northern Ireland are investigated by the Police Ombudsman for Northern Ireland, an external agency which were set up as a result of the Patten report into policing the province.

Investigating crimes committed by the police
There are several types of military police services:

Gendarmeries are military force which polices a civilian population.
Provost services are military police services that work within the armed forces.
Constabulary A civilian police force trained and organized along military lines. Military police
In many jurisdictions, police officers carry firearms, primarily handguns, in the normal course of their duties.
Police often have specialist units for handling armed offenders, and similar dangerous situations, and can (depending on local laws), in some extreme circumstances, call on the military (since Military Aid to the Civil Power is a role of many armed forces). Perhaps the most high-profile example of this was, in 1980 the Metropolitan Police handing control of the Iranian Embassy Siege to the Special Air Service. They can also be equipped with non-lethal (more accurately known as "less than lethal" or "less-lethal") weaponry, particularly for riot control. Non-lethal weapons include batons, riot control agents, rubber bullets and electroshock weapons. The use of firearms or deadly force is typically a last resort only to be used when necessary to save human life, although some jurisdictions allow its use against fleeing felons and escaped convicts. Police officers often carry handcuffs to restrain suspects.
Modern police forces make extensive use of radio communications equipment, carried both on the person and installed in vehicles, to co-ordinate their work, share information, and get help quickly. In recent years, vehicle-installed computers have enhanced the ability of police communications, enabling easier dispatching of calls, criminal background checks on persons of interest to be completed in a matter of seconds, and updating the officer's daily activity log and other required reports on a real-time basis. Other common pieces of police equipment include flashlights/torches, whistles, and police notebooks and "ticketbooks" or citations.

Police armament and equipment

Main article: Police car Police vehicles
The advent of the police car, two-way radio, and telephone in the early 20th century transformed policing into a reactive strategy that focused on responding to calls for service.

Policing strategies
In many nations, criminal procedure law has been developed to regulate officers' discretion, so that they do not arbitrarily or unjustly exercise their powers of arrest, search and seizure, and use of force. In the United States, Miranda v. Arizona led to the widespread use of Miranda warnings or constitutional warnings. Police in the United States are also prohibited from holding criminal suspects for more than a reasonable amount of time (usually 72 hours) before arraignment, using torture to extract confessions, using excessive force to effect an arrest, and searching suspects' bodies or their homes without a warrant obtained upon a showing of probable cause. Using deception for confessions is permitted, but not coercion. There are exceptions or exigent circumstances such as an articulated need to disarm a suspect or searching a suspect who has already been arrested (Search Incident to an Arrest). The Posse Comitatus Act severely restricts the use of the military for police activity, giving added importance to police SWAT units.
British police officers are governed by similar rules, particularly those introduced under the Police and Criminal Evidence Act 1984, but generally have greater powers. They may, for example, legally search any suspect who has been arrested, or their vehicles, home or business premises, without a warrant, and may seize anything they find in a search as evidence. All police officers in the United Kingdom, whatever their actual rank, are 'constables' in terms of their legal position. This means that a newly appointed constable has the same arrest powers as a Chief Constable or Commissioner. However, certain higher ranks have additional powers to authorize certain aspects of police operations, such as a power to authorize a search of a suspect's house (section 18 PACE) by an officer of the rank of Inspector, or the power to authorize a suspect's detention beyond 24 hours by a Superintendent.

Restrictions upon the power of the police
Investigation of police corruption is sometimes made more difficult by a code of silence that encourages unquestioning loyalty to comrades over the cause of justice. If an officer breaks this code, they may receive death threats or even be left for dead, as in the case of Frank Serpico. One way to fight such corruption is by having an independent or semi-independent organization investigate, such as (in the United States) the Federal Justice Department, state Attorneys General, local District Attorneys, a police department's own internal affairs division, or specially appointed commissions. However, independent organizations are generally not used except for the most severe cases of corruption.

Police conduct and accountability
Police forces also find themselves under criticism for their use of force, particularly deadly force. Specifically, tension increases when a police officer of one race harms or kills a suspect of another race. In the United States, such events routinely spark protests and accusations of racism against police.
In the United States since the 1960s, concern over such issues has increasingly weighed upon law enforcement agencies, courts and legislatures at every level of government. Incidents such as the 1965 Watts Riots, the videotaped 1991 beating by Los Angeles Police officers of Rodney King, and the riot following their acquittal has depicted American police as dangerously lacking in appropriate controls. The fact that this trend has occurred contemporaneously with the rise of the US civil rights movement, the "War on Drugs" and a precipitous rise in violent crime from the 1960s to the 1990s has made questions surrounding the role, administration and scope of authority of police specifically and the criminal justice system as a whole increasingly complicated. Police departments and the local governments that oversee them in some jurisdictions have attempted to mitigate some of these issues through community outreach programs and community policing to make the police more accessible to the concerns of local communities; by working to increase hiring diversity; by updating training of police in their responsibilities to the community and under the law; and by increased oversight within the department or by civilian commissions. In cases in which such measures have been lacking or absent, local departments have been compelled by legal action initiated by the US Department of Justice under the 14th Amendment to enter into consent decree settlements to adopt such measures and submit to oversight by the Justice Department.
Some believe that police forces have been responsible for enforcing many bigoted perspectives. Ageism against teens, classism, homophobia, racism, and sexism are views which police have been charged with having held and enforced. Some police organizations are faced with routine accusations of racial profiling.

Use of force
The social status and pay of police can lead to problems with recruitment and morale. Jurisdictions lacking the resources or the desire to pay police appropriately, lacking a tradition of professional and ethical law enforcement, or lacking adequate oversight of the police often face a dearth of quality recruits, a lack of professionalism and commitment among their police, and broad mistrust of the police among the public. These situations often strongly contribute to police corruption and brutality. This is particularly a problem in countries undergoing social and political development; countries that lack rule of law or civil service traditions; or countries in transition from authoritarian or Communist governments in which the prior regime's police were little more than praetorians.

Police around the world