Feline Interleukin-5 (IL-5) is a Th2-associated cytokine produced primarily by activated CD4⁺ T helper 2 (Th2) cells, mast cells, and group 2 innate lymphoid cells in cats (Felis catus), where it plays a central role in eosinophil differentiation, activation, recruitment, and survival. IL-5 is part of the common beta chain (βc) cytokine family, which also includes IL-3 and granulocyte–macrophage colony-stimulating factor (GM-CSF); these cytokines share the βc receptor subunit and are involved in regulation of hematopoiesis and myeloid cell function. IL-5 signals through a receptor complex composed of IL-5Rα and the shared βc chain, activating JAK/STAT and MAPK pathways that promote eosinophil maturation in the bone marrow and enhance their effector functions in peripheral tissues. In feline health, IL-5 is particularly important in eosinophil-associated diseases such as feline asthma, eosinophilic granuloma complex, allergic dermatitis, food hypersensitivity, and parasitic infections, where elevated IL-5 contributes to eosinophilic airway inflammation, dermal lesions, and tissue remodeling. While IL-5–mediated responses support protective immunity against helminths, excessive or chronic IL-5 expression can drive persistent eosinophilic inflammation and tissue damage. As a biomarker of type 2 immune activation and eosinophilic disease, feline IL-5 is relevant in studies of allergic pathogenesis, vaccine responses, and immune modulation. In translational research, cats serve as valuable spontaneous models for human asthma and eosinophilic airway disorders, and characterization of feline IL-5 supports comparative investigations into βc cytokine signaling and development of targeted anti–IL-5 therapeutic strategies relevant to both veterinary and human medicine.