Apoptotic signals are transduced by five death domain-containing receptors--TNFR1, Fas, DR3, DR4, and DR5--by binding to their ligands. The intracellular portion of all these receptors contains a region, approximately 80 amino acids long, referred to as the "death domain" (DD). On activation by its ligand, the DD recruits various proteins that mediate cell death. These proteins, in turn, recruit other proteins via their DDs or death effector domains (DED). The actual destruction of the cell, however, is accomplished by serial activation of a family of proteases referred to as caspases. Cell death is, in part, regulated by transmembrane decoy receptors that contain either none of or only part of the DD. This article briefly reviews what is known about the receptors and other proteins involved in apoptosis. In addition, because numerous proteins that mediate apoptosis have been discovered independently and simultaneously and thus are known by many different names, a comprehensive cross-referenced list of these proteins is provided.