This volume contains I. Bernard Cohen and Anne Whitman’s 1999 translation of Newton’s Principia. In the preface and in the notes to the translation, Cohen refers to his “Guide to Newton’s Principia” (“the Guide”). This volume contains an excerpt from the Guide (“A Brief History of the Principia”). The Guide appears in full in The Principia: The Authoritative Translation and Guide, also available from University of California Press.