This book provides a comprehensive analysis of the use of peace agreements from a legal perspective. It describes and evaluates the development of contemporary peace processes and the peace agreements that emerge. The book sets out what is in essence an anatomy of peace agreement practice and interrogates its relationship to law. At its heart the book grapples with the role of law in ending violent conflict and the broader questions this raises for the relationship of law to social change. Law potentially plays two key roles with respect to peace agreements: first, to the extent that peace agreements themselves form legal documents, law plays a role in the 'enforcement' or implementation of the peace agreement; second, international law has a relationship to peace agreement negotiation and content, in its regulatory guise. International Law regulates self-determination, transitional justice, and the role of third parties. The book documants and analyses these two roles of law. In doing so, the book reveals a complex dynamic relationship between the peace agreement as a legal document and the role of international law in which international law and concepts of domestic constitutionalism are being re-shaped. The practice of negotiating peace agreements is argued to be producing a new law of the peacemaker-or lex pacificatoria that connects developments in international law with new forms of domestic constitutional law in a set of hybrid relationships. This law of the peacemaker potentially forms part of a broader 'law of peace' that moves beyond the traditional concept of law of peace as merely 'the rest of international law' once the laws of war are subtracted. The new lex pacificatoria stands as an account of the way in which international law shapes and is shaped by peace agreements. The book proposes an ambivalent response to 'this new law' which connects to contemporary debates about the force of international law and its appropriate relationship with domestic constitutonalism.