The Moscow Peace Treaty was signed by Finland and the Soviet Union on 12 March 1940, and the ratifications were exchanged on 21 March. It marked the end of the 105-day Winter War, upon which Finland ceded border areas to the Soviet Union. The treaty was signed by Vyacheslav Molotov, Andrei Zhdanov and Aleksandr Vasilevsky for the Soviet Union, and Risto Ryti, Juho Kusti Paasikivi, Rudolf Walden and Väinö Voionmaa for Finland. The terms of the treaty were not reversed after the dissolution of the Soviet Union. The Karelian question refers to the debate within Finland over the possible reacquisition of this ceded territory.

The Finnish Democratic Republic, also known as the Terijoki Government, was a short-lived communist puppet state of the Soviet Union in occupied Finnish territory from December 1939 to March 1940.