Asthma and rhinosinusitis with nasal polyps are highly prevalent chronic airway diseases that cause high morbidity and socio-economic burden worldwide, without a definitive cure. Hypereosinophilic syndromes sometimes associated with vasculitis are orphan, yet life threatening diseases. Eosinophils (EOs) have been developed in evolution to kill parasites, yet accumulate in all these diseases, and are thought to be harmful by releasing of granules and crystals.  This led to development of drugs targeting EOs. However, our consortium recently discovered that there are also “beneficial EOs” with immunoregulatory potential, that might be important for immune defense in cancer and infections like COVID-19.  We hypothesize that the true functionof EOs is highly context dependent and can only be unraveled if we move away from the simple “eosin staining cell” to a detailed and integrated immunophenotyping, single cell and biomarker approach in the blood and tissue of residence of the eosinophil, combined with a detailed clinical phenotyping and patient response to treatment. The BENEFICIARIES consortium brings together the best basic science and clinical groups working on eosinophilic diseases in Belgium, and combines structural biology, multi-omics techniques, mouse genetics and molecular and cellular immunology to study clinically relevant questions. This will deliver new insights,high quality intellectual property and new diagnostics and therapeutics to eosinophilic disorders.