This book provides a comprehensive and in-depth study of Physics I, the first book of Aristotle's foundational treatise on natural philosophy. While the text has inspired a rich scholarly literature, this is the first volume devoted solely to it to have been published for many years, and it includes a new translation of the Greek text. Book I introduces Aristotle's approach to topics such as matter and form, and discusses the fundamental problems of the study of natural science, examining the theories of previous thinkers including Parmenides. Leading experts provide fresh interpretations of key passages and raise new problems. The volume will appeal to scholars and students of ancient philosophy as well as to specialists working in the fields of philosophy and the history of science.