This book provides the first variorum translation into English of Isaac Newton’s De Motu Corporum in Gyrum, from the 1685 manuscript at Cambridge University Library (UCL Add. 3990). It offers a unique perspective on the development of Newton’s views on a number of critical issues before the publication of the first edition of the Principia in 1687. The book fills a critical gap in Newton scholarship. The translation deliberately reflects the vocabulary and syntax of Newton’s Latin as closely as possible, enabling the reader to track the text in the manuscript almost word-by-word, including the ubiquitous inserts and deletions that show where and how Newton changes his mind or struggles with the formulation of a point.