Isidore (Russian: Исидор; died 1462) was Metropolitan of Moscow and all Russia.

In 1437, Isidore was appointed Metropolitan of Kiev and Moscow by John VIII Palaeologus to draw the Russian Orthodox Church into the union with the Roman Catholic Church and secure Constantinople's protection against the Ottoman Turks. Vasili II met the new Metropolitan with hostility. However, Isidore managed to convince the Grand Prince to ally with Catholicism for the sake of saving the Byzantine Empire and the Greek Church.

After Isidor had received funding from Vasili II, he went to Florence to attend an ecumenical council in 1439. He was made a cardinal-presbyter and a papal legate for the provinces of Lithuania, Livonia, all Russia and Galicia (Poland). During this holy meeting, Isidore was fervently defending the union between the Churches, but he was opposed by the only secular representative from Russia - ambassador Foma (Thomas) of Tver. Finally, the union agreement was signed and Isidor went to Russia.

The Russian princes denounced the union, but Isidor persisted. On his return from Italy, during his first divine service in the Cathedral of the Dormition in the Moscow Kremlin, Isidor was ordered to carry a Catholic cross in front of the ceremony, pray for the Pope during the mass, and read aloud the union agreement. Isidor passed a message to Vasili II from Pope Eugenius IV, containing a request to assist the Metropolitan in spreading Catholicism in Russia. Three days later Isidor was arrested and placed in the Chudov Monastery. He was condemned by the Russian clergy for refusing to repent and renounce the union.

In September of 1441, Isidor fled to Tver, then to Lithuania and Rome. In 1458, he was ordained as a nominal Patriarch of Constantinople.