Apoptosis is the process of programmed cell death. It plays critical roles in development and immunity, as well as cancer and neurodegenerative disease. Apoptosis is accompanied by complex cascades of intracellular events that may include the activation of pro-apoptotic Bcl-2 family members, members of the Caspase family, and several nucleases. This leads to characteristic cellular changes including transfer of phosphatidylserine to the outer leaflet, chromatin condensation and DNA degradation, membrane blebbing, and ultimately the formation of apoptotic bodies that can be efficiently cleared by phagocytes. Apoptosis can be initiated via several mechanisms including trophic factor withdrawal, ligation of pro-apoptotic transmembrane receptors, or the activities of cytotoxic immune cells.