Mobility and migration were not uncommon in Byzantium, as is true for all societies. Yet, scholarship is only beginning to pay attention to these phenomena. This book presents in English translation a wide array of relevant source texts from ca. 650 to ca. 1450 originally written in medieval Greek: from administrative records, saints' lives and letters by churchmen to ego-documents by ambassadors and historical narratives by court historians. Each source text is accompanied by a detailed introduction, commentary and further bibliography, thus making the book accessible to both scholars and students and laying the groundwork for future research on the internal dynamics of Byzantine society.