This chapter outlines the rationale, methods, and theoretical foundations of the book. The author argues that Japan, as the first non-Western nation to industrialise, offers a historically unique model for late developers. Its history of development cooperation should be reconstructed through the voices of recipients rather than those of donors. The first section explains why oral evidence from local counterparts—engineers, teachers, doctors, officials, etc.—is essential for capturing how Japan’s projects were implemented on the ground. It describes the author’s fieldwork across 16 projects in Asia, Africa, and Latin America, and reflects on the nature of oral testimony and its subjectivity. The following sections develop the theoretical framework. Building on the concept of ‘teaching how to fish’ and applying the principal-agent framework to development practice, the chapter sheds light on the ultimate objectives of international cooperation. It distinguishes between colonial, cooperative, and solidarity models of development assistance. Finally, drawing on A.O. Hirschman’s principle of ‘Hiding Hand’, the chapter views crises—political, environmental, and institutional—as catalysts for the dynamic transformation of development projects. The last section explains how the case studies in this book are logically structured.