H. L. A. Hart’s book, The Concept of Law, is perhaps the single greatest contribution to the field of legal philosophy in this century. Hart lays the groundwork for the continued progress in the perennial debate between legal positivism and natural law. This book briefly reviews the historic significance of that debate and demonstrates how Hart paves the way for an enlightened analysis of the tenuous relationship between law and morality. It provides a detailed examination of Hart’s efforts to establish a legal framework through primary and secondary rules and an ultimate rule of recognition. It focuses specifically on Hart’s reliance on the internal perspective as a means of establishing the form of obligation necessary for a legal system. It examines Hart’s treatment of the relationship between law and morality and Hart’s mischaracterization of St. Thomas Aquinas’s natural law theory.