Part I Anastasius Bibliothecarius, papal librarian, translator and diplomat, is one of the pivotal figures of the ninth century in both literary and political contexts. His contribution to relations between the eastern and western church can be considered to have had both positive and negative ramifications, and it will be argued that his translations of various Greek works into Latin played a significant role in achieving his political agenda, complex and convoluted as this was. Being one of relatively few Roman bilinguals in the latter part of the ninth century, Anastasius found that his linguistic skills opened an avenue into papal affairs that was not closed by even the greatest breaches of trust and violations of canonical law on his part. His chequered career spanning five pontificates will be reviewed in the first chapter. In Chapter 2, we discuss his corpus of works of translation, in particular the Collectanea, whose sole surviving witness, the Parisinus Latinus 5095, has been partially edited in this study. This collation and translation of seven documents pertaining to the life of Maximus the Confessor provides us with a unique insight into Anastasius' capacity as a translator, and into the political and cultural significance of the commissioning and dedication of his hagiographic and other translated works in general. These seven documents will be examined in detail in Chapter 3, and compared with the Greek tradition, where that has survived, in an effort to establish the codes governing translation in this period, and to establish which manuscripts of the Greek tradition correspond most closely to Anastasius' (lost) model. In Chapter 4, we analyse consistency of style and method by comparison with Anastasius' translation of the Historia Mystica attributed to Germanus of Constantinople. Anastasius' methodology will be compared and contrasted with that of his contemporary John Scotus Eriugena, to place his oeuvre in the broader context of bilingualism in the West in the ninth century. Part II contains a critical edition of the text with facing English translation and historical and linguistic annotations.