The Hexaemeron by St Basil of Caesarea was a fundamental source for Christian writers describing the nature of the physical cosmos, not least in Armenia, where scholars attempted to reconcile theories derived from Greek antiquity with the Bible. The first part of this volume is a survey of references to Basil in Armenian writers from the fifth to the fourteenth centuries, and more particularly of the influence of the Hexaemeron on their cosmology. The second part is an English translation of the Armenian version. The commentary to the translation identifies the expansions and changes made by the Armenian translator, and justifies numerous divergences from the text of the critical edition Erevan 1984] in favour of readings also attested in the Syriac version Leuven 1995, CSCO 550], for the Armenian derives from the latter, not directly from the Greek. There are detailed Indices for the Armenian, Greek, Syriac and Latin sources quoted, the Armenian technical terms, and the topics discussed by Basil. The translations of the Hexaemeron in Syriac, Armenian, Arabic, Georgian and Old Slavonic contain only the original nine homilies, not the further two on the creation of man later added by Basil's brother, Gregory of Nyssa.