Previous commentators on the Metaphysics have attributed to Aristotle the belief that all living beings are substances. This book challenges the prevailing view by addressing the question of whether, according to Aristotle, artifacts are substances. By arguing that the two criteria of substantiality are "eternity" and "actuality" (thereby excluding some organisms), and by covering Aristotle's theory of art and nature as well as his embryology, Aristotle on Artifacts offers a novel way of dealing with a number of highly controversial issues and variety of metaphysical problems.