Fas (CD95) is a member of the death receptor (DR) family, a subfamily of the tumor necrosis factor receptor superfamily. The formation of the Fas death-inducing signaling complex (DISC) is the initial step of Fas signaling. Activation of procaspase-8 at the DISC leads to the induction of DR-mediated apoptosis. Stimulation of Fas has been also reported to trigger non-apoptotic pathways. It has been shown that membrane-bound FasL is essential for the cytotoxic activity, whereas soluble FasL appears to promote autoimmunity and tumorigenesis via induction of non-apoptotic pathways, in particular NF-kappa.