This thesis presents an investigation of the nature of the earliest extant records of the supposed communication with angels and spirits of John Dee (1527-1608) with the assistance of his two mediums or 'scryers', Barnabas Saul and Edward Kelly. The form chosen is a transcription of the records in Dee's hand contained in Sloane MS 3188, together with an introduction and commentary to the text, which has been transcribed only once before, by Elias Ashmole in 1672. In the Introduction the physical state of the manuscript is described and a hypothesis advanced as to how it arrived in the Sloane collection. Biographical details of Dee and his scryers are provided and a further chapter presents some background to Renaissance occult philosophy and the practice of scrying. Arguments that the manuscript represents a conscious fraud or a cryptographical exercise are examined and disproved and the magical system and instruments evolved during the communications or 'Actions' are described. The last chapter of the Introduction examines Dee's motives for believing so strongly in the truth of the Actions and suggests that a principal motive was the conviction, not held by Dee alone, that a new age was about to dawn upon earth. The Commentary aims primarily at explaining the many obscurities of the text.