During the Cold War, the term Eastern Bloc (or Soviet Bloc) was used to refer to the Soviet Union and countries it either controlled or that were its allies in Central and Eastern Europe (Bulgaria, Czechoslovakia, East Germany, Hungary, Poland, Romania, and—until the early 1960s—Albania).

The label "Eastern Bloc" was also used to collectively denote member states of the Warsaw Pact (a Soviet-dominated military organisation) or the Comecon (an international economic organization of Communist states). Soviet allies outside of Eastern Europe, such as Mongolia and often China, Cuba, Vietnam, Ethiopia, and North Korea were sometimes included in the term Eastern Bloc as well.

The terms Eastern Bloc and Soviet Union are sometimes confused. Although the Soviet Union had much political and economic influence over its Eastern Bloc possessions, the other countries in the Eastern Bloc were never constituent republics of the Soviet Union.