David Lewis's work is of fundamental importance in many areas of philosophical inquiry and there are few areas of Anglo-American philosophy where his impact has not been felt. Lewis's philosophy also has a rare unity: his views form a comprehensive philosophical system, answering a broad range of questions in metaphysics, philosophy of mind, philosophy of language, philosophy of action and many other areas. This breadth of Lewis's work, however, has meant that it is difficult to know where to start in Lewis's work and a casual reader may often miss some of the illuminating connections between apparently quite disparate pieces of Lewis's work. This book aims to make this body of work more accessible to a general philosophical readership, while also providing a unified overview of the many contributions Lewis has made to contemporary Anglo-American philosophy. The book can be divided into four parts. The first part examines Lewis's metaphysical picture - one of the areas where he has had the greatest impact and also the framework for the rest of his theories. The second section discusses Lewis's important contributions in the philosophy of mind, language and meaning. The third part explores some of Lewis's work in decision theory, metaethics and applied ethics, areas where his work in not necessarily as widely appreciated, but in which he has done a range of work that is both accessible and important. The final section focuses on Lewis's distinctive philosophical method, perhaps one of his most significant legacies, which combines naturalism with "common-sense" theorizing.