Intelligence system or apparatus is a term which implies institutionalization and organization of implementation of the intelligence activities of a country or another actor. The intelligence system of socialist Yugoslavia has its beginnings before the implementation of the revolution and the creation of the „Second Yugoslavia“. Namely, the intelligence activity was carried out illegaly by the action platforms of the Communist Party of Yugoslavia, and later these efforts were institutionalized in the form of the Department for the Protection of the People (OZNA), the State Security Directorate (UDBA) and the Counterintelligence Service (KOS), the Information and Documentation Directorate (UID), the Information and Documentation Service (SID), and later the State Security Service (SDB) and the Military Security Service. This intelligence system was entirely at the service of the Communist party of Yugoslavia and the preservation of the regime. The services that made up this intelligence system played a decisive role in the collapse of the Socialist Federal Republic of Yugoslavia (SFRJ), and they retained a reduced influence in the successor states.