The EXIMIOUS factsheets was developed within the EU-funded EXIMIOUS project as part of their toolbox. The factsheets present different types of populations used to investigate how occupational and environmental exposures contribute to immune-mediated diseases. The tool provides an overview of the population used in the project, which includes general population, birth cohorts, worker cohorts, and cohorts of patients affected by immune-mediated diseases. The Factsheet Tool has been created by researchers on behalf of the 15 EXIMIOUS project partners. It is primarily intended for researchers in epidemiology and clinical fields who wish to reuse the high-quality data collected in EXIMIOUS. However, it is also valuable for teaching purposes, offering accessible examples of different cohort types, and for stakeholder events where it can help clarify the basis of immune-related research. Each factsheet gives a concise summary of a specific population, detailing its size, relevance to immune-mediated diseases, and the types of data and measurements collected.