Equine 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 regulation of humoral immunity in horses (Equus caballus). BAFF is produced primarily by monocytes, macrophages, dendritic cells, neutrophils, 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 maintenance of long-lived plasma cells. In healthy horses, BAFF supports normal antibody production and immune homeostasis in systemic and mucosal tissues, including the respiratory and gastrointestinal tracts. Dysregulated or elevated BAFF expression may contribute to chronic inflammation, autoantibody production, and B cell proliferation in conditions such as equine recurrent uveitis, equine asthma, inflammatory bowel disease–like syndromes, and lymphoid malignancies. In veterinary and comparative medicine research, equine BAFF is of particular interest in studies of vaccine-induced antibody responses, mucosal immunity, autoimmune disease models, and comparative B cell biology. Characterizing BAFF signaling in horses provides valuable insight into regulation of humoral immunity and potential therapeutic strategies targeting B cell–mediated disease in equine and translational research contexts.