The Codex epistolaris Carolinus preserves ninety-nine letters, dated between 739 and 791 and sent by the popes to the Frankish king Charlemagne and his predecessors. The compilation was commissioned by Charlemagne in 791, but the sole surviving medieval manuscript of the letters was made at Cologne in the later ninth century and is now in Vienna (OEsterreichische Nationalbibliothek Cod. 449). The headings or lemmata provided for each letter by the Frankish compilers in 791 and faithfully preserved in the codex, add a distinctive Frankish commentary on events in Rome and Italy in the second half of the eighth century. This book not only provides the first full English translation of the letters and lemmata in the Codex epistolaris Carolinus but also re-creates the original Carolingian order of presentation of the letters according to the manuscript. A substantial introduction discusses the historical significance of the collection, the compilation and contexts of the Vienna manuscript, especially the significance of the lemmata, the peculiarities of the Latin of the papal letters and the biblical citations, and the historical context of the letters themselves. The lemmata and letter translations are augmented with introductions to each letter and a comprehensive historical commentary and glossary.