This book is the first full-length study of the LXX column of the Complutensian Polyglot Bible (1514–17), the editio princeps of the LXX. It investigates the sources and editorial method of the Hellenists who edited the Polyglot’s LXX column and clarifies many of the enigmatic characteristics of the Complutensian LXX. The LXX column is an eclectic text constructed by a number of editors who worked semi-independently towards a common goal. Individual Hellenists, working more in parallel than as a ‘team’ in the contemporary sense, edited sections of a biblical book, each bringing his particular philological skill to bear. Close examination of their editorial choices shows the differing linguistic knowledge of the editors. All knew Latin and Greek but not all - maybe only one - knew Hebrew, Latin and Greek. When this difference in knowledge is combined with their semi-independent modus operandi, the textual variation in the Greek column becomes more understandable and the character of its text less enigmatic. The marked variation from volume to volume, from book to book and, at times, within individual books, has its roots both in the different MS sources and the varying editorial styles. This study refines the identification of sources from earlier investigations of vols. 1-3, and confirms the use of a very close congener of Pap. 967 as one of the constant sources for Ezekiel in vol. 4. For vol. 4, the search for sources and the attempt to understand the editorial method together permit the recognition of extensive editorial use of the LXX lemmata from Jerome’s In Hiezechielem in establishing the LXX column thereby identifying the final contributing factor in the uneven and enigmatic character of the Ezekiel text. This provides a new framework for the investigation of the remaining prophetic texts in vol. 4, and permits the evaluation of many of the more characteristic readings in that volume. In this light we best appreciate the nature of the fidelity accorded their MS sources by the Hellenists of Alcalá. When two MSS are available, one is used as primary source, which is corrected from the other or secondary source, with the editor changing primary sources at various points. Vg is used as a guide in establishing the text, especially in the overall shape of the text. Consequently, the influence of Vg must always be determined. MT has less influence, as only one of the two principal editors knew Hebrew, but it plays a role in some omissions and in straightforward choices among variants. Thus with the reduction in the borrowing from the secondary source and in the number of readings attributable to spontaneous editorial intervention and with a new appreciation of the quality of some of the MS sources, the editorial activity of the Complutensian Hellenists may be seen in a much calmer light. The Complutensian Polyglot is a monument not only to those who produced it but also to its culture and its time. This study permits the Polyglot’s LXX column to provide a window on the scholarship and intellectual culture of early modern Spain by showing how the Hellenists of Alcalá emended their source MSS. Placing the Greek Old Testament column of the Complutensian Polyglot Bible within the history of editions of the Greek OT, it provides a clear direction for further research.