This book is an account of Aristotle’s Metaphysics. The work is considered as a whole and each of its parts or books is taken up in the order that it has in the traditional text. The book is based on an examination of all of the manuscript readings reported in the three most recent editions of the work (those of Christ, Ross, and Jaeger), and it attempts in this way and others to come as close as possible to what would have been the original text. The Metaphysics is of course a much-studied work. What distinguishes this new effort to understand it is the working assumption that Aristotle presents in it his most comprehensive reflection on science: its character and aims, its foundations or presuppositions, and the obstacles or objections that constitute a challenge to its possibility. The book is thus intended to be of interest and use to at least two classes of readers: to those who have already reflected themselves on the nature of science and who have perhaps become dissatisfied with more recent attempts to establish it on a firm basis or to explain the basis on which it rests; and to beginning students who are willing to undertake a difficult task and who can be brought to see that science and philosophy were originally equivalent terms and that the effort to distinguish or separate them may have been deeply misguided. In other words, the book is meant to afford a glimpse into what philosophy originally meant.