The immune system provides many examples of cell populations that are susceptible to the induction of apoptosis. Self-reactive immature cells are deleted by triggering apoptosis. Additionally, mature peripheral lymphocytes are induced to undergo apoptosis, particularly when hyperactivated. In the past few years, several genes have been linked to cell death in lymphoid cells. However, only a handful of these genes has been shown to be required for cell death to occur in the immune system. This review focuses on signals known to mediate apoptosis in the immune system and those genes demonstrated to be required for the induction of cell death.