This unit attempts to define cell toxicity that leads to cellular demise, with a strong emphasis on cell death via both apoptosis and necrosis, by summarizing some of the more recent developments in cellular, molecular, and biochemical studies of the events that govern the induction and execution of cell death. Specific topics pertaining to cell death include structural changes, macromolecular degradation, cellular signaling, the role of mitochondria, and genetic modulation of apoptotic cell death.