In an era marked by externalisation, destination states often engage in complex arrangements with transit states, international organisations, and private actors to avert the arrival of protection-seekers at their territories. The heterogeneity and multiplicity of actors involved in such arrangements challenges the framework of international responsibility, which fails to hold all actors responsible for their contribution to a refoulement. This chapter introduces the book’s objective to provide guidance to academics, judges and practitioners grappling with the complex task of determining the shared responsibility of multiple international persons that contribute through their wrongful conduct to a refoulement. It lays the groundwork for an in-depth analysis on how the law of international responsibility—as reflected in the International Law Commission’s articles on the international responsibility of states and international organizations, and as novelly interpreted in the Guiding Principles on Shared Responsibility in International Law—struggles to accommodate scenarios of multi-actor involvement in a refoulement and on how the limitations of this framework can be addressed. The chapter also sets out the methodological basis for the analysis in the subsequent chapters and situates the book’s contribution within the existing literature.