Islam has engaged the attention of Christians ever since its rise in Arabia in the seventh century. One obvious reason is the fact that most early Muslim conquests took place within Christian lands. “The People of the Book,” as Jews and Christians were called, faced the choice of adopting the faith of their conquerors, or of remaining in their particular religion. Those who persisted in their Christian commitment gave a reason for this decision. They could not, and would not forsake the biblical Messiah, their Lord and Savior. By implication, they refused to believe in the “heavenly” mission of Muhammad who claimed to be God’s final messenger commissioned to call the world to Islam. From the beginning of the Christian-Muslim encounter, the main debate centered on these fundamental teachings: the authenticity of the Christian Scriptures, the person and work of Jesus Christ, and the doctrine of the Holy Trinity.