THIS book was prepared as lectures to be given on the Gunning Foundation in connection with the Divinity Hall of Edinburgh University. As actually delivered in the spring of this year the lectures had to be severely compressed. They are now printed in the form in which they were written. I am indebted to the Faculty of Divinity for the opportunity of treating a subject in which I have long been interested. A special word of thanks is due to Professor A. R. S. Kennedy, D.D., to whose teaching, advice and encouragement I owe much. One of the objects of the Gunning Bequest is to "bring out among ministers the fruits of study in Science, Philosophy, Language, Antiquity, and Sociology". If any restriction is implied in that wide definition it is that the subject of study should not be directly theological. The primary interest of these lectures is historical. The aim has been to present the origin of Islam against a background of surrounding Christianity. In some ways that point of view has proved more fruitful than I had expected. Instead of discovering, as I set out to discover, what was the nature of the contact which Muhammad had had with Christianity before he began the composition of the Qur'an, I found