The tumor necrosis factor ( TNF ) family is a group of cytokines with multiple biological activities, including cytotoxity, anti-viral activity, immunoregulatory activities and so on. The members of the TNF family induce apoptosis by binding to their specific receptors on target cells and initiate mechanism of apoptosis in the cells. Some proteins like TRADD, FADD, RIP, TAIDD are found to participate in these signal transduction pathways. More and more novel TNF ligands, TNF receptors and caspase family members have been found.