In this substantially revised second edition, Neil MacCormick delivers a clear and current introduction to the life and works of H.L.A. Hart, noted Professor of Jurisprudence at Oxford University from 1952 to 1968. Hart established a worldwide reputation through his powerful philosophical arguments and writings in favor of liberalizing criminal law and applying humane principles to punishment. This book demonstrates that Hart also made important contributions to analytical jurisprudence, notably by clarifying many terms and concepts used in legal discourse, including the concept of law itself. Taking into account developments since the first edition was published, this book provides a constructively critical account of Hart's legal thought. The work includes Hart's ideas on legal reasoning, judicial discretion, the social sources of law, the theory of legal rules, the sovereignty of individual conscience, the notion of obligation, the concept of a right, and the relationship between morality and the law. MacCormick actively engages with current scholarly interpretations, bringing this accessible account of England's greatest legal philosopher of the twentieth century up-to-date.