Aging causes the immune system to become less effective, increasing susceptibility to infections and age-related diseases. Researchers at the Leibniz Institute on Aging have created a comprehensive molecular and cellular map of immune aging in a vertebrate using the short-lived turquoise killifish. Using a multi-omics approach, they identified key features of immune aging, including chronic inflammation, DNA damage in progenitor cells, and remodeling of the hematopoietic organ. The study shows that important aspects of immune aging are evolutionarily conserved. This makes the killifish particularly well suited for studying the mechanisms of immune aging and testing potential interventions.