The Brezhnev Doctrine was a Soviet policy that was created by Leonid Brezhnev in 1968.

"When forces that are hostile to socialism and try to turn the development of some socialist country towards capitalism, it becomes not only a problem of the country concerned, but a common problem and concern of all socialist countries." - Leonid Brezhnev

It was put in place originally to justify the invasion of Czechoslovakia to crush the Prague Spring. In essence, it meant that no country was permitted to leave the Warsaw pact and that the Soviet government had the right to intervene in the government of other socialist states. This policy was extended past Eastern Europe and the country annually bailed out countries such as Afghanistan, Cuba, Nicaragua, and Vietnam.

The policy drained the country and in 1988 Mikhail Gorbachev officially abandoned it and replaced it with the Sinatra Doctrine. The Sinatra Doctrine allowed Warsaw pact countries to manage their own affairs without Soviet assistance, which was one of the factors in the ending of the Cold War.

Sources:
http://www.wikipedia.org/
http://www.search.eb.com/ebi/article?eu=295137&query=brezhnev%20doctrine
http://asia.cnn.com/SPECIALS/cold.war/kbank/profiles/brezhnev/