The Communist Party of the Soviet Union (Russian: Коммунисти́ческая Па́ртия Сове́тского Сою́за, transliterated Kommunisticheskaya Partiya Sovetskogo Soyuza, acronym: КПСС (KPSS)) was the ruling political party in the Soviet Union. It emerged in 1912 as the Bolshevik faction of the Russian Social-Democratic Labour Party created a separate party. The party led the October Revolution, which led to the establishment of a socialist state in Russia. The party was dissolved in 1991, at the time of the breakup of the Soviet Union.

For most of the history of Soviet Russia and the Soviet Union, the Communist Party was virtually indistinguishable from the government, as it was generally the only political party tolerated by the government. Consequently, the history of the USSR and the CPSU are deeply intertwined and overlapping. Therefore, it is useful for those interested in the history of the CPSU to also consult the History of Russia series of articles.