This book is the product of a major British Academy Symposium held in 2007 to mark the centenary of the birth of H.L.A. Hart, the most important legal philosopher and one of the most important political philosophers of the twentieth century. The book brings together contributions from seventeen of the world's foremost legal and political philosophers who explore the many subjects in which Hart produced influential work. Each essay engages in an original analysis of philosophical problems that were tackled by Hart, some essays including extended critical discussions of his major works: The Concept of Law, Punishment and Responsibility, Causation in the Law and Law, Liberty and Morality. All the main topics of Hart's philosophical writings are featured: general jurisprudence and legal positivism; criminal responsibility and punishment; theories of rights; toleration and liberty; theories of justice; and causation in the law.