As of summer 2019, more than 60 PIAAC datasets from participating countries worldwide were available for research purposes. These datasets can be differentiated, for example, in terms of their accessibility, the extent of the information provided, the population group in focus, and the design of the underlying study. PIAAC Public Use Files, for instance, are freely available and are therefore highly anonymised, whereas PIAAC Scientific Use Files are available only for scientific research purposes and provide access to more detailed variables. The majority of the PIAAC data are available as public use files, but some participating countries (e.g. Germany and the United States) have also made several scientific use files or other extended file versions available to the research community. Some of the available PIAAC datasets focus on specific population groups-for example, the incarcerated adult population in the United States. Regarding the design of the underlying studies, most available datasets are cross-sectional, but some longitudinal data already exist (e.g. PIAAC-L in Germany). The present chapter provides an overview of the structure, accessibility, and use of the PIAAC datasets available worldwide. 4.1 Overview of PIAAC Data Available for Secondary Analysis Based on the PIAAC data, diverse interdisciplinary questions-such as social inequality, competency and ageing issues, and the role of digitalisation-can be investigated in an internationally comparable way, thereby addressing genuine political demands. PIAAC data contain information about basic skills (literacy, numeracy, and problem solving in technology-rich environments) that are considered to be prerequisites for understanding specific domains of knowledge in a broad