The Warsaw Pact invasion of Czechoslovakia refers to the events of 20–21 August 1968, when the Czechoslovak Socialist Republic was jointly invaded by four Warsaw Pact countries: the Soviet Union, the Polish People's Republic, the People's Republic of Bulgaria and the Hungarian People's Republic. The invasion stopped Alexander Dubček's Prague Spring liberalisation reforms and strengthened the authoritarian wing of the Communist Party of Czechoslovakia (KSČ).

About 250,000 Warsaw Pact troops (afterwards rising to about 500,000), supported by thousands of tanks and hundreds of aircraft, participated in the overnight operation, which was code-named Operation Danube. The Socialist Republic of Romania and the People's Republic of Albania refused to participate, while East German forces, except for a small number of specialists, were ordered by Moscow not to cross the Czechoslovak border just hours before the invasion because of fears of greater resistance if German troops were involved, due to the previous German occupation. 137 Czechoslovaks were killed and 500 seriously wounded during the occupation.

Public reaction to the invasion was widespread and divided. Although the majority of the Warsaw Pact supported the invasion along with several other communist parties worldwide, Western nations, along with Albania, Romania, and particularly the People's Republic of China condemned the attack. Many other communist parties lost influence, denounced the USSR, or split up or dissolved due to conflicting opinions. The invasion started a series of events that would ultimately see Brezhnev establish peace with United States President Richard Nixon in 1972 after the latter's historic visit to China.

After the invasion, Czechoslovakia entered a period known as normalization, in which new leaders attempted to restore the political and economic values that had prevailed before Dubček gained control of the KSČ. Gustáv Husák, who replaced Dubček as First Secretary and also became President, reversed almost all of the reforms.