Gerasimus I (Greek: Γεράσιμος, Gerasimos; died 19 April 1321)^[1] was the Ecumenical Patriarch of Constantinople from 1320 to 1321.^[2]

He was born in Philadelphia and became abbot of the prestigious Mangana Monastery in Constantinople. He was elected as patriarch at an advanced age, and died on 19 April 1321.

He became Patriarch during the reign of Emperor Andronicus the Second; the Emperor found him to be 'docile'.^[3]

• Gerasimus of the Jordan, 5th century saint
• Gerasimus I of Jerusalem, 19th century Patriarch of Jerusalem
• Gerasimus of Kefalonia, patron saint of Kefalonia, Greece