The Thesis is in three parts and is concerned with providing an introduction to, and an analysis and text of the extant manuscript minutes of Sessions 45 to 73 of the Westminster Assembly of Divines 1640. These unpublished minutes are now deposited at the Dr. Williams Library, London, and are records of the debates of the Assembly while they were engaged in revising some of the Thirty-nine Articles of Religion of the Church of England. The introduction to the text covers the Parliamentary activity which led to the calling of the Assembly, and deals with the relations of Parliament with Scotland, which gave so much direction to the work of the Assembly and led to the Solemn League and Covenant. The composition of the Assembly and the rules by which the Assembly was regulated, are also examined. The introduction concludes with an analysis of the discussions of the Assembly as recorded in the defined sessions. The second part of the thesis consists of an analysis of each session dealt with. This became necessary as each of the transcribed sessions was found to be difficult to understand as the scribe had employed a highly individual form of theological shorthand, and had missed out vital parts of complicated arguments. In the analysis most of the arguments of the original text have had to be amplified to make sense. The third part of the thesis comprises of the transcription of the text of the minutes. The original exists only in manuscript form, and the illegibility of some parts is exaggerated by the use of the unique theological shorthand of Adoniram Byfield, the scribe. In the transcription all punctuation and capitalization have been supplied though original spellings have been preserved. Though the transcription has been compared with that of Sir E.M. Thompson deposited at New College Library, Edinburgh, it has been necessary to depart from many of the interpretations of that transcription. There are three Appendices attached to the thesis, the first compares the revised and unrevised Articles dealt with in Sessions 45 yo 73. The second provides biographical information on continental authorities cited in debates. The third provided a bibliographical guide to those members who participated in the debates on the revision.