Secondary data represent a vital components in the toolkit of social scientists. Among them, panel and longitudinal data are especially valuable for observing changes within a sample population over time. This chapter aims to highlight the power of these data sources by which social scientists can uncover valuable insights that inform policy decisions, shape interventions, and contribute to our understanding of the world. To be more effective and useful for the purposes of use by public institutions or academies and research institutions in the extemporaneous reading of social phenomena, the characteristic of the speed with which the phenomena studied are detected and analyzed constitutes a significant added value which makes Research Infrastructures on longitudinal and panel data in social science, unique in its kind, and is inserted into a lack of information that is crucial.