All investigations into the prosopography of the Byzantine world are shaped by three key concerns. Who to include? Which geographical regions to study? Which sources to scrutinize? As the contributors to this volume demonstrate, these are particularly pressing and difficult questions for the prosopographer of the post1204 Byzantine world given the political fragmentation of Byzantium in the later twelfth and early thirteenth centuries, and the emergence of new socio-political structures, many of them dominated by those with alternative ethnic and religious identities. But the fact that there are no easy answers to these questions should not deter attempts to execute a full prosopography of the Byzantine world in this period. Indeed, if anything, the studies in this volume demonstrate that active engagement with these definitional problems can make for a more sophisticated prosopography with the capacity to help us answer that elusive question of just what it meant to be Byzantine. This, of course, is a question with which many scholars have recently been wrestling from a variety of perspectives, particularly with reference to the later Byzantine centuries.1