Feline Interleukin-6 (IL-6) is a multifunctional pro-inflammatory cytokine and a central member of the IL-6 cytokine family, which includes IL-6, IL-11, IL-27, IL-31, leukemia inhibitory factor (LIF), oncostatin M (OSM), ciliary neurotrophic factor (CNTF), cardiotrophin-1 (CT-1), and cardiotrophin-like cytokine factor 1 (CLCF1), all of which signal through receptor complexes that utilize the shared gp130 subunit. In cats (Felis catus), IL-6 plays a critical role in regulating acute-phase protein production, hematopoiesis, B- and T-cell differentiation, and systemic inflammatory responses via the IL-6R/gp130-mediated JAK/STAT pathway. Dysregulation of IL-6 and related family members contributes to the pathogenesis of infectious diseases such as feline infectious peritonitis (FIP) and feline immunodeficiency virus (FIV), as well as chronic inflammatory conditions, immune-mediated disorders, and certain neoplasms. Elevated IL-6 levels are associated with fever, increased serum amyloid A production, and disease severity, making it a valuable biomarker for inflammation and treatment monitoring in veterinary medicine. In animal model research, characterization of feline IL-6 and its related cytokine family members supports investigation of cytokine-driven pathology, immune signaling networks, and host-pathogen interactions, while also enhancing comparative and translational studies, as naturally occurring feline diseases provide important models for understanding IL-6 family-mediated mechanisms relevant to human inflammatory and infectious diseases.