This book examines how subnational actors use international human rights treaties and how subnational political authorities, including subnational legislators, come to engage with international treaties. In this chapter, we present our empirical approach, our research design, methods and data. We outline how we combine top-down and bottom-up perspectives, building on scholarship from law, political science and socio-legal studies. We explain and justify the selection of the treaties under investigation and the procedure of data collection for the Swiss case.