Today law is a popular subject at universities and colleges. Although people who study subjects like mathematics, music, biology or history will have studied them before while at high school, and know something of the elements and methods of their chosen subject, that is not true of those who study law as a specialist subject. This book is aimed at introducing the subject to newcomers. It has also been written to be of use as a continuing companion to legal study, and of being helpful, I hope, to other citizens. The number and range of law books, law reports and legislative volumes in the library has grown considerably over the years. In his inaugural lecture at Oxford on 21 April 1883, the distinguished constitutional lawyer A.V. Dicey noted that even until well into the nineteenth century it was possible for a person to read the entirety of English law within the compass of an ordinary adult life. It could be contained in fewer than 200 volumes. Today, an earnest reader would probably need to live for over 600 years to read all law and regulations applicable in the United Kingdom. Whether that would be the most edifying way to spend a 600-year life is another matter. This book is about both the hardware and software of law. It is about the tangible parts of the enterprise, like lawyers, judges, the dramas of courtrooms, and juries – the hardware. It is also about the theories inexplicitly, and thus invisibly, relied on in law when, for example, cases are analysed or legislation is interpreted and applied – the software.