The Karelo-Finnish Soviet Socialist Republic (Finnish: Karjalais-suomalainen sosialistinen neuvostotasavalta; Russian: Каре́ло-Фи́нская Сове́тская Социалисти́ческая Респу́блика, tr. Karelo-Finskaya Sovetskaya Sotsialisticheskaya Respublika), or, in short, Karelo-Finnish SSR (Finnish: Karjalais-suomalainen SNT; Russian: Каре́ло-Фи́нская ССР), was a short-lived republic that was a part of the former Soviet Union. The republic existed from 1940 until it was merged into the Russian SFSR in 1956 (as the Karelian Autonomous Soviet Socialist Republic).
The Karelo-Finnish Soviet Socialist Republic was set up on March 31, 1940 by merging the KASSR with the Finnish Democratic Republic (created in territory ceded by Finland in the Winter War by the Moscow Peace Treaty, namely the Karelian Isthmus and Ladoga Karelia, including the cities of Viipuri and Sortavala). The entire Karelian population of the ceded areas, about 422,000 people, was evacuated to Finland, and the territories were settled by people from other parts of the Soviet Union.