The internal affairs refers to a division of a law enforcement agency that investigates incidents and possible suspicions of law-breaking and professional misconduct attributed to officers on the force. It is thus a mechanism of limited self-governance, "a police force policing itself". In different systems, internal affairs can go by other names such as internal investigations division (usually referred to as IID), professional standards, inspectorate general, Office of Professional Responsibility, internal review board, or similar.
Due to the sensitive nature of this responsibility, in many departments, officers employed in an internal affairs unit are not in a detective command but report directly to the agency's chief, or to a board of civilian police commissioners.
Internal affairs investigators are bound by stringent rules when conducting their investigations. In California, the Peace Officers Bill of Rights (POBR) is a mandated set of rules found in the Government Code.
The internal affairs function is not an enforcement function, but rather a policing function that works to report only. The concept of internal affairs is very broad and unique to each police department. However, the sole purpose to having an internal affairs unit is to investigate and find the truth to what occurred when an officer is accused of misconduct. An investigation can also give insight on a policy itself that may have issues.
The circumstances of the complaint determine who will be investigating the complaint. The investigation of alleged misconduct by police officers can be conducted by the internal affairs unit, an executive police officer, or an outside agency. In the Salt Lake City Police Department, the Civilian Review Board will also investigate the complaint, but they will do so independently. When the investigation begins, everything is documented and all employees, complainants, and witnesses are interviewed. Any physical evidence is analyzed and past behaviors of the officer in question are reviewed. Dispatch tapes, police reports, tickets, audio, and videotapes are all reviewed if available. Many controversies arise because an officer investigating police misconduct may show favoritism and/or hold grudges particularly when a single officer is conducting the investigation. Some departments hire uninvolved officers or include another department or a special unit to conduct the investigation.
Larger agencies have the resources to have separate units for internal affairs, but smaller agencies - which do not have the luxury - are more common, with 87% of police departments in the United States employing 25 or fewer sworn officers. Smaller agencies that do not have sufficient resources may have the executive officer, the accused's supervisor, or another police department conduct an investigation. The state police may also be asked to investigate criminal behavior, but they do not deal in minor misconduct or rule violation cases. However, allowing another department to investigate can result in lower morale among the officers because it can appear as an admission that the department cannot handle their own affairs.
Several police departments in the USA have been compelled to institute citizen review or investigation of police misconduct complaints in response to community perception that internal affairs investigations are biased in favor of police officers.
For example, San Francisco, California, has its Office of Citizen Complaints, created by voter initiative in 1983, in which citizens who have never been members of the San Francisco Police Department investigate complaints of police misconduct filed against members of the San Francisco Police Department. Washington, DC, has a similar office, created in 1999, known as the Office of Police Complaints.
In the state of Utah, the Internal Affairs Division must properly file a complaint before the committee can officially investigate. Complaints involving police misuse of force will be brought to the Civilian Review Board, but citizens can request the committee to investigate any other issues of misconduct.