The Christian belief in the Trinitarian nature of God has come under criticism from Muslims who are convinced that the oneness of God is compromised by the Christian assertion that God is Father, Son and Holy Spirit. Throughout nearly fourteen hundred years of relations between Muslims and Christians, Muslims have challenged Christians to agree with them that God is one. Christians have responded by saying that they hold to the oneness of God who reveals himself in threeness without sacrificing his oneness. This book examines Christian attempts to present the Trinity to Muslims along with Muslim reactions to these efforts. Part One deals with communication by Middle Eastern Christians with Muslims after the Arab armies took over the Middle East in the seventh century up to the thirteenth century. Part Two studies the writing of mainly Western Christians who began to take dialogue with Muslims seriously from the nineteenth century until today. The reader will be able to see Christian presentations alongside Muslim responses to gain a comprehensive view of dialogue on the nature of God between Muslims and Christians.