International migration is often characterised as a process of immigration from economically less developed to highly developed countries. Whereas the factors driving those flows and the integration of the respective ethnic groups are widely analysed, the international mobility of the populations of precisely those affluent societies is regularly missed and less-frequently studied. The chapter describes the research design of the German Emigration and Remigration Panel Study as one of the first endeavours to study the internationally mobile populations from prosperous welfare states. Following an origin-based probability sampling of internationally migrating German citizens, it offers survey data to study the consequences of emigration and remigration along the life course. The chapter discusses the quality of this new data infrastructure along the survey lifecycle and compares the distribution of central demographic characteristics in the survey with official reference statistics. The aim is to establish this approach as a new avenue for studying the global lives of internationally mobile populations.