Athenagoras, the late-second-century apologist, was almost unknown in Christian antiquity and has not attracted much attention from modern scholars. This study examines systematically what is known of his life, his works, his background in Greek philosophy and in the Biblical and Christian tradition. His doctrines of God, of the Logos-Son, the Holy Spirit and the Trinity are discussed as is his doctrine of Creation and of man. His knowlege of the Church and liturgy is shown to be more extensive than has beensometimes thought. Finally his strong emphasis on the Christian life and his witness to the moral goodness found among Christians from all classes of society are shown to be convincing proofs of the difference Christianity has made by its coming into the Graeco-Roman world. The author argues that the value of Athenagoras' work lies in his sensitivity to the intellectual currents of his time which he sought to adapt to the service of the Christian faith.