The NKVD (Narodny Komissariat Vnutrennikh Del) (Russian: НКВД, Народный комиссариат внутренних дел) or People's Commisariat for Internal Affairs was the leading secret police organization of the Soviet Union that was responsible for political repressions during Stalinism. It ran the Gulag system of forced labor, deported nations and peasants labeled as "Kulaks" to unpopulated regions of the country, guarded state borders, conducted espionage, and political assassinations abroad and was responsible for subversion of foreign governments, and enforcing Stalinist policy within Communist movements in other countries.

The NKVD is best known for the Main Directorate for State Security (GUGB).

In addition to its state security and police functions, however, some of its departments handled other matters, such as transport, fire guards, border guard (NKVD Border Troops), etc., the tasks that were traditionally assigned to the Ministry of the Interior (MVD).

Although the NKVD performed the function of state security, the name of the organization today is associated primarily with its criminal activities: political repressions and assassinations, military crimes, violations of the rights of Soviet and foreign citizens, and violation of the law.