This will be the first of two volumes of collected studies by the well-known German historian of the Crusades, Professor H. E. Mayer. Each volume will cover different aspects of his research. In the present one he examines the source material upon which any study of the Crusader States must be based. The documents dealt with throw much light on, for instance, their relations with the powers of Western Europe, and include several which concern the Church and the religious institutions of the Holy Land. The subsequent volume will concentrate more specifically on the monarchy and the nobility of the latin Kingdom of Jerusalem.