Saint Constantine may refer to:
Constantine I (c. 272 – 337), Roman Emperor and a convert to Christianity Constantine of Dumnonia (6th century), King of Cornwall Constantine of Strathclyde (6th century), probably fictitious King of Strathclyde Constantine (British saint), various figures of this name Constantine the Jew (fl. c.850–886), Byzantine monk Constantine XI, last Byzantine emperor, unofficial Catholic Saint St Cyril, born Constantine, Christian theologian from Thessalonica and Christian missionary among the Slavs with his brother Methodius