This encyclopedia entry provides an overview of law governing the police. As it notes, police officers are granted immense authority by the state to impose harm. The problem of policing the police is how to regulate police officers and departments to protect individual liberty and minimize the social costs the police impose while allowing them to do what is necessary to achieve the ends of policing: reducing fear, promoting civil order, and pursuing criminal justice. Constitutional law provides the most well-known check on police conduct. In addition, many other federal, state, and local statutes, constitutional provisions, court decisions, and administrative regulations also govern the police. Since federal constitutional law cannot alone ensure that the benefits of policing are worth the harms it imposes, this participation by other government actors is essential to ensure adequate regulation of the police. However, the laws that presently govern the police are not tailored to balance the individual and societal interests at stake when police officers act, they lack coordination, and responsibility for regulating the police is haphazardly allocated. As a result, the present array of laws that polices American policing does not promote law enforcement that is maximally effective and protective of civil rights. 

Rachel Harmon, Legal Control of the Police, in Encyclopedia of Criminology and Criminal Justice, Springer Reference, 2898–2906 (2014).