Feline BAFF (B cell–Activating Factor), also known as BLyS or TNFSF13B, is a member of the tumor necrosis factor (TNF) superfamily and plays a central role in B cell development, survival, and humoral immunity in cats (Felis catus). BAFF is produced primarily by monocytes, macrophages, dendritic cells, and certain stromal cells, and it signals through the receptors BAFF-R (TNFRSF13C), TACI (TNFRSF13B), and BCMA (TNFRSF17) to promote peripheral B cell maturation, immunoglobulin class switching, and the maintenance of long-lived plasma cells. In healthy cats, BAFF supports normal antibody production and immune homeostasis; however, dysregulated or elevated BAFF expression may contribute to excessive B cell activation and autoantibody production. In veterinary and comparative medicine research, feline BAFF is particularly relevant in naturally occurring diseases such as feline immunodeficiency virus (FIV) infection, feline leukemia virus (FeLV) infection, feline infectious peritonitis (FIP), chronic inflammatory conditions, and B cell–derived malignancies including lymphoma and multiple myeloma. Characterization of feline BAFF provides valuable insight into B cell–mediated immune regulation, chronic infection–associated immune dysregulation, and potential therapeutic strategies targeting BAFF signaling in feline and translational immunology research.