This chapter employs a mixed methods research strategy. It combines the quantitative approach, which is deployed to test hypotheses generated by our theory, and the qualitative approach, which is dedicated to substantiate the theory and assess its assumptions about agents' preferences and behaviours. After a critical review of major branches of social science methodology, the chapter justifies the selection of China and its pension system. Disaggregating China into sub-national units enlarges the number of cases, which allows to use the statistical method to test the implications of our theory. This quantitative approach should be coupled with the qualitative analysis because this is the way through which we can have a comprehensive assessment of the validity of our theory. Advocates of the rational choice approach argue that a theory should be justified on the capacity of its predictions to survive empirical tests rather than on the accuracy of its assumptions. The chapter also presents the research design of this book.