Gelasius, the Nicene bishop of Caesarea Maritima for roughly the last third of the fourth century, has been overshadowed by his more famous uncle and patron Cyril of Jerusalem. Gelasius’ works are preserved only fragmentarily in later authors. The most important of his writings was a church history, which supplemented and continued that of his eminent predecessor Eusebius. Later ecclesiastical historians and hagiographers, such as Rufinus of Aquileia, drew on Gelasius’ history extensively, although usually without attribution. It furnished them with a model for Nicene historiography and with material on topics such as the youth of the emperor Constantine, the discovery of the True Cross in Jerusalem, the Council of Nicaea, and the beginnings of Christianity in Ethiopia and Georgia. The fragments of Gelasius’ Ecclesiastical History are presented here systematically for the fi rst time. They are accompanied by the fragments of his doctrinal writings as well as all known testimonia about the bishop’s life and work. The edition is introduced by a thorough discussion of the sources and includes a facing English translation and notes.