Although the main duties of the police had always been the prevention, detection, and investigation of crime and the maintenance of public order, their involvement under successive governments in suppressing political and labor organizations left a reservoir of fear and mistrust among the Portuguese people. The authority of the police, which was identified with the old regime, was seriously compromised by the Revolution of 1974. During the months after the revolution, there was a sharp rise in crime and disorder owing to the virtual disappearance of social and moral constraints imposed by tradition and reinforced by the authoritarian regime. Until the civilian police forces, disarmed after the revolution, could be reorganized and retrained to operate in Portugal's new political environment, armed forces security units assumed responsibility for internal security. By 1976, control of the police apparatus was returned to civilian authorities in the Ministry of Internal Administration.

Article 272 of the Constitution of 1976, as revised in 1982, emphasized the responsibility of the police to defend the democratic process and to ensure that they acted within the law and did not exceed their authority. In carrying out their mission of preventing crimes, including crimes against the security of the state, the police were enjoined to observe the rights, freedoms, and safeguards of citizens. The constitution stipulated that each of the forces of security were to have a single organization for the entire national territory.

Data as of January 1993