This chapter describes the three purposes the book serves.The first is to introduce readers to certain core questions in the philosophy of law, by way of engagement with international legal skepticism.The book’s second aim is to acquaint readers with recent work by legal and political philosophers on conceptual and moral questions specific to particular domains of international law.These include the nature of human rights, and of a crime against humanity, as well as the moral justifiability of certain core features of the law of war, international trade law, and international law’s stance on unilateral secession.Finally, the book aims to advance the debate on many of the topics it discusses.Examples include novel readings of both H.L.A. Hart’s and Ronald Dworkin’s reflections on international law, as well as new arguments regarding the existence of an international rule of law, the possible bases of a moral duty to obey international law, and the moral grounds of universal jurisdiction over crimes against humanity.A brief chapter-by-chapter outline is also included.