Chicken BAFF (B cell–Activating Factor), also known as BLyS or TNFSF13B, is a member of the tumor necrosis factor (TNF) superfamily and plays an important role in B cell development, survival, and regulation of humoral immunity in chickens (Gallus gallus). BAFF is produced primarily by monocytes, macrophages, dendritic cells, and stromal cells within primary and secondary lymphoid tissues, including the bursa of Fabricius, spleen, and cecal tonsils. Through interaction with its receptors—avian homologs of BAFF-R, TACI, and BCMA—chicken BAFF promotes B cell maturation, immunoglobulin production, and maintenance of antibody-secreting plasma cells. In avian species, BAFF is particularly important for bursal B cell development and mucosal antibody responses, including IgY and IgA production. Dysregulated BAFF expression may be associated with chronic inflammation, viral infections such as infectious bursal disease virus (IBDV) and Marek’s disease virus (MDV), or lymphoid proliferative disorders. In poultry science and comparative immunology research, chicken BAFF is studied in the context of vaccine responses, resistance to enteric and respiratory pathogens, immune system development, and strategies to enhance humoral immunity in commercial poultry production.