Politburo is the name usually given to the supreme agency in Communist countries that sets goals and policies for the Communist party and for the government.
In the Soviet Union, "politburo" is a shortened form for the Political Bureau of the Central Committee of the Soviet Communist party. It first came into being in October 1917 to direct the Bolshevik seizure of power. Lenin, Trotsky, Stalin, Zinoviev, and Kamenev were among its seven members. With the success of the revolution, the Politburo passed out of existence. It was revived by the Eighth Party Congress in March 1919. To prevent it from overshadowing the power of the party's larger Central Committee, from whose membership the Politburo was to be drawn, the Congress required the Politburo to report to the Central Committee on a regular basis and to permit members of the Central Committee to attend its meetings, though with only a consultative vote. A secretariat for the Politburo evolved somewhat later. Stalin became its general secretary in 1922.
The Politburo soon eclipsed the Central Committee in importance. And in turn it was eclipsed by Stalin, who, in the 1920's, rose to his position of unchallenged authority by placing his own men in the party apparatus, the Central Committee, and ultimately in the Politburo. The majority of the Politburo members of 1931 did not survive the Great Purge in the second half of the 1930's.
At the Nineteenth Party Congress, in 1952, the Politburo was replaced by a larger Presidium. On Stalin's death in 1953, its size was reduced. Nikita Khrushchev, party secretary, had become undisputed leader by 1957 by reorganizing its membership. Yet the Presidium was powerful enough to oust him in 1964. Leonid Brezhnev succeeded Khrushchev as first secretary, and in April 1966 the Twenty-Third Congress revived the Politburo. Like his predecessors, Brezhnev consolidated his power by changing its membership, the most dramatic change having taken place in 1973.