This chapter presents the methodology and research design of the multi-country case study of youth transitions in Japan, Germany, Switzerland, the United Kingdom and Norway. After outlining the motivation for the comparative study, the research questions, and assumptions, the multi-country case study design is presented. Positioning Japan as an unique, unusual and critical case in youth transition research, the selection of four European countries for comparison is justified according to country-specific youth transition contexts such as youth welfare citizenship, youth labour market dynamics, and the strength of the male-breadwinner model in each country. The chapter then highlights the analytical strategies for the country case studies and the comparative study in general. This is followed by an overview of the national youth data and the criteria used to make the observations from the different longitudinal and cross-sectional data comparable at two biographical age windows at the end of the first and beginning of the second decade of the new millennium. Finally, the measures of the different types of youth transitions (school-to-work, housing and domestic transitions) and the main variables used in the comparative analysis, such as life satisfaction and the subjective perception of risk, are outlined.