These chapters survey the range of historical sources from the peoples who collided with the Byzantine Empire during this period of dramatic upheaval. The Empire that had been expanded and consolidated by Basil II (d. 1025) was to disintegrate in the face of incursions from the north and Muslim east. In addition, pilgrims and crusaders from the west passed through the Empire and settled – culminating in the capture of Constantinople by the Fourth Crusade in 1204. In order to understand the history of the region during this period, one must be aware of the rich source material created by these shifting populations, in a wide range of languages, and with differing traditions of historical writing. The 14 chapters give an overview of the material, highlighting any problems the historian may have in dealing with it, and provide detailed bibliographical surveys. Latin, Arabic, Jewish, Slavonic, Georgian, Armenian, and Syriac sources are all discussed.