Main Intelligence Directorate (Russian: Главное разведывательное управление, romanized: Glavnoye razvedyvatel'noye upravleniye, IPA: [ˈglavnəjə rɐzˈvʲɛdɨvətʲɪlʲnəjə ʊprɐˈvlʲenʲɪjə]), abbreviated GRU (Russian: ГРУ, IPA: [ɡɨ̞‿rɨ̞‿ˈu], [gru]), was the foreign military intelligence agency of the General Staff of the Soviet Armed Forces until 1991.

The GRU's first predecessor in Russia formed on October 21, 1918 by secret order under the sponsorship of Leon Trotsky (then the civilian leader of the Red Army), signed by Jukums Vācietis, the first commander-in-chief of the Red Army (RKKA), and by Ephraim Sklyansky, deputy to Trotsky;[1] it was originally known as the Registration Directorate (Registrupravlenie, or RU).

[…] As a result of the re-organization [in 1926], carried out in part to break up Trotsky's hold on the army, the Fourth Department seems to have been placed directly under the control of the State Defense Council (Gosudarstvennaia komissiia oborony, or GKO), the successor of the RVSR.

The existence of the GRU was not publicized during the Soviet era, but documents concerning it became available in the West in the late 1920s, and it was mentioned in the 1931 memoirs of the first OGPU defector, Georges Agabekov, and described in detail in the 1939 autobiography of Walter Krivitsky (I Was Stalin's Agent), who was the most senior Red Army intelligence officer ever to defect.

According to Suvorov, even the General Secretary of the Communist Party of the Soviet Union, when entering the GRU headquarters, needed to go through a security screening.

This was a GRU reference to a training film shown to him, in which he alleges he watched a condemned agent being burned alive in a furnace.,[6][page needed] During the Cold War, the Sixth Directorate was responsible for monitoring Intelsat communication satellites traffic.