Book excerpt: No other scholar has so deeply influenced the development of international law or shaped the doctrinal debates as Vattel. More than 250 years after its publication, his Law of Nations has remained the most frequently quoted treatise of international law. Vattel's International Law from a XXIst Century Perspective explores the reasons behind the extraordinary authority of Vattel and analyses its continuing relevance for thinking and understanding contemporary international law. It gathers the contributions from well-known experts of international law and history for the purpose of evaluating the Law of Nations from a XXIst century perspective. The multiple facets of Vattel’s thinking are apprehended through a wide-ranging and comprehensive analysis respectively devoted to the international system, the sources of international law, the subjects of international law, the law of peace, and the law of war.