The study of unilateral and extraterritorial sanctions must be based on a theoretical foundation and clear definitions. The introductory chapter proposes a protean definition of these measures. Starting from a functional definition, the chapter gives the keys to a conceptual definition by questioning in turn the notion of international sanctions, the practice of extraterritoriality in the field of sanctions design, and unilateralism in the field of international sanctions. The introduction then presents the approach followed in the book and the methodology used. International practice is analysed with the help of six case studies, and the corresponding issues in public international law are presented. The chapter then addresses the question of the impact of unilateral and extraterritorial sanctions on economic operators and human rights, and concludes by emphasizing that the international practice of unilateral and extraterritorial sanctions is today at a political, legal and economic crossroads.