Chronology of Soviet security agencies
1917–22	Cheka of the Sovnarkom of the RSFSR (All-Russian Extraordinary Commission)
1922–23	GPU of the NKVD of the RSFSR (State Political Directorate)
1923–34	OGPU of the Sovnarkom of the USSR (Joint State Political Directorate)
1934–41 1941–43	NKVD of the USSR (People's Commissariat for Internal Affairs) GUGB of the NKVD of the USSR (Main Directorate of State Security)
1941 1943–46	NKGB of the USSR (People's Commissariat for State Security)
1946–53	MGB of the USSR (Ministry of State Security)
1953–54	MVD of the USSR (Ministry of Internal Affairs)
1954–91	KGB of the Council of Ministers of the USSR (Committee for State Security)

The People's Commissariat for State Security (Russian: Народный комиссариат государственной безопасности, romanized: Narodnyy komissariat gosudarstvennoy bezopasnosti) or NKGB, was the name of the Soviet secret police, intelligence and counter-intelligence force that existed from 3 February 1941 to 20 July 1941, and again from 1943 to 1946, before being renamed the Ministry for State Security (MGB).

Changes in Soviet apparatus began in February 1941 with the Presidium of the Supreme Soviet decision. It started with Military Counterintelligence. On 3 February 1941, the 4th Department (Special Section, OO) of GUGB within the NKVD security service responsible for the Red Army military counter-intelligence, consisting of 12 Sections and one Investigation Unit, was separated from the GUGB NKVD. The official liquidation of the OO GUGB and GUGB as organized units within the NKVD was announced on 12 February 1941 by a joint order № 00151/003 of the NKVD and NKGB USSR.
The rest of the GUGB was abolished and staff were moved to the newly created People's Commissariat for State Security (NKGB). Departments of the former GUGB were renamed Directorates. For example, the former Foreign Department (INO) became the Foreign Directorate (INU); political police represented by the Secret Political Department (SPO) became the Secret Political Directorate (SPU), and so on.

Based on NKVD and NKGB directive number 782/B265M, from 1 March 1941, the NKGB tasks were:

• Conducting intelligence activities abroad;
• Battling espionage (on both fronts: counter and offensive);
• Battling sabotage and terrorist acts organized by foreign Special Services on USSR territory;
• The penetration, and liquidation, of anti-Soviet parties and counter-revolutionary organizations;
• Overseeing ideology in Soviet society;
• The protection of high party and government officials.

The first head of NKGB was Vsevolod Nikolayevich Merkulov who became People's Commissar of State Security. His first deputy was Ivan Serov, a former Commissar 3rd rank of State Security, and two deputies, Bogdan Kobulov and Mikhail Gribov.

The Soviet security organizations were merged in July 1941, after the German invasion, with the NKGB Directorates returned to NKVD as separate units. During 1943 changes NKGB was created again as separate Commissariat. Please look at organization changes below)

These organizational changes were never explained. According to historian John Dziak they may have had something to do with the Soviet occupations of Latvia, Lithuania, Estonia, eastern Poland, part of Romania (Bessarabia and northern Bukovina). Also, the numbers of apprehensions, deportations, executions and establishments of Gulags had quickly grown, which required a reorganization of structures and a boost of manpower in the security administration. Other reasons Dziak states are: the shock caused by the German aggression and the fast progress of their army; and when the Soviet victory in Stalingrad had made prospects of the recovery of previous war losses more likely.^[1]

In 1946, other changes followed. Existing People's Commissariats were renamed "ministries." People's Commisariat for Internal Affairs (or NKVD) was renamed Ministry of Internal Affairs (Ministerstvo Vnutrennikh Del) or MVD, and the People's Commissariat for State Security was renamed Ministry for State Security (Ministerstvo Gosudarstvennoi Bezopasnosti) or MGB.

• Bibliography of Stalinism and the Soviet Union
• Chronology of Soviet secret police agencies
• Eastern Bloc politics
• RSHA

• Vadim J. Birstein : SMERSH Stalin's Secret Weapon, Soviet military counterintelligence in ww2 ISBN 978-1-84954-108-4
• Piotr Kołakowski – NKWD i GRU na ziemiach Polskich 1939–1945 – (Kulisy wywiadu i kontrwywiadu) – Dom wydawniczy Bellona Warszawa 2002 – (NKVD and GRU on Polish soil 1939–1945 [Intelligence counter-intelligence series] Warsaw, 2002)
• Norman Polmar, Thomas B Allen – Spy Book: The Encyclopedia of Espionage 1997