The following pages present a brief outline of the history of the Fatimid Khalifs who were ruling in Egypt at the time of the First and Second Crusades. Too often the student of European history gleans his knowledge of the oriental powers with which the West was brought into contact by the Crusades from western Christian writers, who do not fairly or truly describe those powers, and do not set forth clearly the strong and weak points which are so important in interpreting the actual forces with which the Crusaders were brought into contact. These pages are drawn from the Arabic and Persian historians so as to present a picture which, though inaccurate in some points, nevertheless shows the other side not perceived by the historians who wrote the narrative of the Crusades from a western standpoint. Directly, therefore, they supplement the western history, but are still more important in their indirect bearing as an effort has been made to show the rise and development of the Fatimid Khalifate and sect as a rival to the orthodox Abbasid Khalifate of Baghdad, which is most essential to the right understanding of the world into which the Crusaders penetrated, whilst at the same time it shows a curious and important phase of Muslim tendencies which are not without a bearing on the later history of Islam. The present essay does not claim to be an original study in a field hitherto unexplored, but simply aims at bringing together in an accessible form material which will be of service to the student of mediaeval western history and to those who are interested in the development of Islam, and to do so with such comments as will enable it to be co-ordinated with contemporary European history.