Canine 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 dogs (Canis lupus familiaris), where it plays a central role in eosinophil differentiation, activation, recruitment, and survival. IL-5 is a member 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 regulate 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 activity in peripheral tissues. In canine health, IL-5 is particularly important in eosinophil-associated diseases such as eosinophilic bronchopneumopathy, atopic dermatitis, food hypersensitivity, parasitic infections, and certain gastrointestinal inflammatory conditions, where elevated IL-5 contributes to eosinophilic infiltration, tissue inflammation, and remodeling. While IL-5–mediated responses support protective immunity against helminths and other parasites, excessive or chronic IL-5 expression can drive persistent inflammation and tissue damage. As a biomarker of type 2 immune activation and eosinophilic disease, canine IL-5 is relevant in allergy research, vaccine evaluation, and immune modulation studies. In translational research, dogs serve as valuable spontaneous models for human asthma and eosinophilic disorders, and characterization of canine 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.