WThe Azerbaijan Communist Party was the ruling political party in the Azerbaijan SSR, making it effectively a branch of the Communist Party of the Soviet Union. It was formed on 20 February 1920, when the Muslim Social Democratic Party, Communist Party of Persia, Agrar Party and Baku Bolsheviks joined together to establish the Communist Party of Azerbaijan. On 1 April of the same year, the Fifth Cabinet of Ministers of the Azerbaijan Democratic Republic gave its resignations and all the power to the Communist Party of Azerbaijan. The party ruled the Azerbaijan SSR until 14 September 1991 when it was formally disbanded. Nevertheless, former leaders and members of the communists continued to play a role in the family- and patronage-based political system. The Communist Party of Azerbaijan won the first multi-party elections in Azerbaijan that took place on 30 September and 14 October 1990 for the Supreme Soviet obtaining 280 out of 360 seats.
WThe Communist Party of Byelorussia was the ruling communist party of the Byelorussian Soviet Socialist Republic, a constituent republic of the Soviet Union from 1922, that existed from 1918 to 1993.
WThe Communist Party of Estonia was a political party in Estonia.
WThe Communist Party of the Karelo-Finnish SSR, initially known as the Communist Party (Bolshevik) of the Karelo-Finnish SSR, was the branch of the All-Union Communist Party/Communist Party of the Soviet Union in the Karelo Finnish SSR 1940–1956.
WThe Communist Party of Kazakhstan was the ruling and sole legal political party in the Kazakh SSR.
WThe Communist Party of Kirghizia was the ruling political party and the section of the Communist Party of the Soviet Union in the Kirghiz Soviet Socialist Republic.
WThe Communist Party of Latvia was a political party in Latvia.
WThe Communist Party of Lithuania is a communist party in Lithuania. The party was established in early October 1918 and operated clandestinely until it was legalized by Soviet authorities in 1940. The party was banned in August 1991, following the collapse of the Soviet Union and the dissolution of the Lithuanian SSR.
WThe Communist Party of Tajikistan is a communist party in Tajikistan, and the oldest political party in the country.