The edition of the 57 letters in the existing fragment of the third volume of Pope Innocent III's chancery registers, covering the period from September 1200 to February 1201, closes the gap that had existed for a long time in the edition of chancery registers of one of the most important medieval popes, published by the Österreichisches Historisches Institut in Rome and the Institut für Österreichische Geschichtsforschung in Vienna. This replaces the deficient text of the Patrologia Latina edited by Migne with a critical edition that meets all scholarly requirements and follows the pattern of the 14 volumes of the existing register edition. In addition to the careful edition of the text according to the original manuscript in the Archivio Apostolico Vaticano (Reg. Vat. 5), a detailed critical apparatus with German summaries, previous prints, identification of places and persons and the historical background, references to Canon and Roman law, identification of the biblical quotations occurring in the text and other textual models serves this purpose. The letters were sent throughout the entire Christian world of the time, from Scandinavia to Southern Italy, from Ireland to the Byzantine Empire. The announced forthcoming second part will contain the reconstruction of the missing part of the register covering the third year of Innocent' s pontificate.