The Main Directorate of the General Staff of the Armed Forces of the Russian Federation, formerly the Main Intelligence Directorate, and still commonly known by its previous abbreviation GRU, is the foreign military intelligence agency of the General Staff of the Armed Forces of the Russian Federation tasked with advancing military intelligence through collecting and analyzing intelligence from around the world and conducting clandestine and covert operations. The GRU controls the military intelligence service and maintains its own special forces units.

Unlike Russia's other security and intelligence agencies – such as the Foreign Intelligence Service (SVR), the Federal Security Service (FSB), and the Federal Protective Service (FSO) – whose heads report directly to the president of Russia (see Intelligence agencies of Russia), the director of the GRU is subordinate to the Russian military command, reporting to the Minister of Defence and the Chief of the General Staff.

The directorate is reputedly Russia's largest foreign intelligence agency, and is distinguished among its counterparts for its willingness to execute riskier "complicated, high stakes operations". According to unverified statements by Stanislav Lunev, a defector from the GRU, in 1997 the agency deployed six times as many agents in foreign countries as the SVR, and commanded some 25,000 Spetsnaz troops.

The first Russian body for military intelligence dates from 1810, in the context of the Napoleonic Wars raging across Europe, when War Minister Michael Andreas Barclay de Tolly proposed to Emperor Alexander I of Russia the formation of the Expedition for Secret Affairs under the War Ministry (Russian: Экспедиция секретных дел при военном министерстве); two years later, it was renamed the Special Bureau (Russian: Особая канцелярия).

In 1815, the Bureau became the First Department under the General Chief of Staff. In 1836, the intelligence functions were transferred to the Second Department under the General Chief of Staff. After many name-changes through the years, in April 1906, the Military intelligence was carried out by the Fifth Department under the General Chief of Staff of the War Ministry.

The GRU's first predecessor in Soviet Russia was established by the secret order signed on 5 November 1918 by Jukums Vācietis, the first commander-in-chief of the Red Army (RKKA), and by Ephraim Sklyansky, deputy to Leon Trotsky, the civilian leader of the Red Army. (Since 2006, the Russian Federation has officially observed the date of 5 November as the professional holiday of military intelligence in Russia.) The military human intelligence service thus established was originally known as the Registration Agency (Registrupravlenie, or Registrupr; Russian: Региструпр) of the Field Headquarters of the Revolutionary Military Council of the Republic; Simon Aralov was its first head. Its early history was marked by a series of reorganisations influenced by the Soviet-Polish War, the consolidation and restablisation of the Soviet Union, and the general reorganisation of the Red Army; this included changes to its name, status, and responsibilities.

Throughout most of the interwar period, the men and women who worked for Red Army Intelligence called it either the Fourth Department, the Intelligence Service, the Razvedupr, or the RU. […] As a result of the re-organisation [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. Thereafter its analysis and reports went directly to the GKO and the Politburo, apparently even bypassing the Red Army Staff.

— Raymond W. Leonard