Eusebius of Caesarea (d. 339), bishop, church historian, and biographer of Constantine, is the major Christian witness to the Constantinian settlement. Despite his importance, his biblical exegesis has not received the attention it deserved. His Commentary on Isaiah, rediscovered in nearly complete form only this century, was written shortly after the Council of Nicaea in 325 and the unification of the empire under Constantine. It is thus an important witness to Eusebius' thinking on the Bible, the church, and the empire at a critical moment in his life and in the history of Christianity. The present book is the first comprehensive assessment of the commentary's methods and ideas. It examines how the new situation influenced Eusebius' reading of Isaiah, especially as revealed in his treatment of Judaism and Jewish exegesis. It also proposes that the commentary's focus on the `godly polity', meaning above all the church and its clergy, is a valuable corrective to interpretations of Eusebius' theology based too exclusively on the Constantinian literature.