Swine 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 pigs (Sus scrofa), Fas ligand is primarily expressed on activated T lymphocytes, cytotoxic T cells, and natural killer (NK) cells, where it interacts with its receptor Fas (CD95) on target cells. Binding of FasL to Fas activates the extrinsic apoptotic pathway, triggering caspase-mediated signaling cascades that induce programmed cell death. In swine immunity, the Fas–FasL system plays an important role in cytotoxic T-cell–mediated elimination of virus-infected or abnormal cells and in maintaining immune homeostasis by removing activated or autoreactive lymphocytes. Because pigs share important physiological and immunological similarities with humans, they are widely used as translational animal models for immunology and transplantation research, and Fas–FasL signaling has been studied in porcine models of organ transplantation, where Fas-mediated apoptosis contributes to regulation of alloreactive immune responses and mechanisms of graft rejection or tolerance, providing insights relevant to human transplant immunology and immune regulation.