This volume about the history of the Ecumenical Patriarchate results from a congress, held in Vienna within the framework of research on the Register of the Patriarchate of Constantinople at the Division of Byzantine Research of the Austrian Academy of Sciences. Chronologically, these papers cover the (Byzantine) period from the 11th century onwards. The majority of the collected studies concern a crucial source: the Register of the Patriarchate of Constantinople. This includes more than 800 documents written between 1315 and 1402 by or for the Patriarchate and the “permanent Synod” of Constantinople, and is now held in the Austrian National Library, Cod. hist. gr. 47 and 48. Besides the Register, the evidence for the Patriarchate is confined to a small number of documents, synodical acts, and occasional references in narrative histories. However, the present volume brings two new texts to light. The focus of this volume is on the organization and administration of the Ecumenical Patriarchate, as well as on new biographical details of individual patriarchs. It also includes contributions devoted to the continuity of the Ecumenical Patriarchate and its new tasks in the early post-Byzantine period.