Digitalization has changed virtually every aspect of the health sector. Enormous amounts of health data are now generated almost by default and stored continuously by various organizations and institutions, which can be very useful for health research. In addition, the sharing and re-use of data is playing an ever-increasing role in science, which is also evident in the recognition of the FAIR principles. These state that scientifically usable data should be FAIR (findable, accessible, interoperable, and reusable). Although some secondary and registry data sources are findable and accessible, full implementation of the FAIR principles requires more effort. At the same time, the international landscape of such data is very diverse and difficult to survey. Moreover, the advantages and potential of using these data have not yet been fully exploited. In this chapter, we will give an overview of important secondary data sources and registries available in Germany, Europe, and worldwide, highlight the advantages of using secondary and registry data for public health research, and provide an overview of methodological requirements and possibilities using record linkage. Finally, we provide perspectives on the use of secondary and registry data for digital public health to enable a widespread FAIRification of health data.