Members in the TNF superfamily regulate immune responses and induce apoptosis. A novel member in the TNF family was recently identified by several groups and designated BAFF, BLyS, TALL-1, THANK, and zTNF4. BAFF/BLyS was characterized as a B cell activator since it induced B cell proliferation and immunoglobulin secretion. Two receptors, TACI and BCMA, for BAFF were originally identified. A third receptor was identified recently and designated BAFF-R and BR3 for BLyS receptor 3. Unlike BCMA and TACI, which bind to BAFF and April, BAFF-R/BR3 is specific for BAFF and plays a predominant role in BAFF induced B cell development and survival. BAFF and its receptors are involved in B cell associated autoimmune diseases, and activate NF-κB and c-jun N-terminal kinase.