This sixth edition of Law and Economics arrives as the field celebrates its (roughly) 30th birthday. What began as a scholarly niche has grown into one of the most widely used tools of legal analysis. The subject has spread from the United States to many other countries. As scholarship deepens, the concepts in the core of law and economics become clearer and more stable, and new applications develop from the core like biological species evolving through specialization. With each new edition, we continue to refine the explanation of the analytical core and to incorporate new applications selectively as space permits. This edition expands previous discussions of empirical legal studies and behavioral law and economics. As we incorporate new material and respond to the suggestions that so many people have sent us, the book feels more like a symphony and less like a duet. We hope that you enjoy reading this book as much as we enjoyed writing it. The book continues to cover the economic analysis of the law of property, torts, contracts, the legal process and crimes. Instructors and students who have used previous editions will notice that we have reversed the order in which we treat torts and contracts, and we have divided the material on legal process into two chapters—one on theory and one on topics—in parallel with our treatment of all the other substantive areas of the law. Below we describe what is new in this edition, followed by an account of the book’s website.