Kerr and colleagues (II) coined the term" apoptosis" to designate a particular form of cell death distinct from necrosis. The salient features of apoptosis, which Kerr defined in histopathologic terms, were the breakup of individual cells into smaller, often round or ovoid cytoplasmic fragments containing pyknotic nuclear debris, called" apoptotic bodies," which were subsequently phagocytized, usually by adjacent cells. This minireview focuses the attention of main molecular pathways of apototis, as default cellular mechanism to maintain physiologic cell number in tissues.