Bovine Fas Ligand (FasL, CD95L, gene FASLG) is a type II transmembrane protein belonging to the tumor necrosis factor (TNF) superfamily, which includes related ligands such as TNF-α, TRAIL (TNFSF10), and CD40L (CD154) that regulate immune signaling, inflammation, and apoptosis. In cattle (Bos taurus), Fas ligand is expressed primarily on activated T lymphocytes, natural killer (NK) cells, and some immune regulatory cells, where it interacts with its receptor Fas (CD95) on target cells. Binding of FasL to Fas triggers the extrinsic apoptotic pathway, activating caspase signaling cascades that lead to programmed cell death. In bovine immunity, the Fas–FasL system plays an important role in regulating immune homeostasis by eliminating infected, damaged, or excess immune cells, helping control immune responses and prevent excessive inflammation. This pathway is also involved in cytotoxic T-cell–mediated killing of virus-infected or abnormal cells during infection. In bovine health, Fas ligand activity contributes to immune regulation during infectious diseases and inflammatory conditions, and dysregulation of Fas–FasL signaling may influence immune-mediated tissue damage or impaired immune control of infection. Because apoptosis and immune regulation are highly conserved processes, bovine Fas ligand is studied in comparative immunology and veterinary infectious disease research to better understand immune cell apoptosis, cytotoxic immune mechanisms, and host–pathogen interactions in livestock species.