This chapter examines the previous research in Section 1.1, clarifies methodology of the present study in Section 1.2, and describes the structure of the book in Section 1.3. It also characterizes Manabu Sato’s educational research, which led to school reform for School as Learning Community (SLC), as an “action research”, and clarifies the significance of conducting case studies of five pilot schools that led school reform for SLC in Japan, based on action researcher Donald A. Schön and Joseph P. McDonald’s “theory-of-action approach” as a methodology for school reform research. Their theory of action in school reform comprises three facets: “espoused theory”, “design theory”, and “theory in use”.