I. Introduction DEATH, along with growth and differentiation, is a critical part of the life cycle of a cell. Homeostatic control of cell number is thought to be the result of the dynamic balance between cell proliferation and cell death. It is only in the past few years, however, that attention has been focused on the physiological occurrence of cell death and its role in homeostasis. Researchers have become increasingly more aware during this time that this type of “natural” death, which is now called apoptosis or programmed cell death, is a widespread phenomenon that plays a crucial role in a myriad of physiological and pathological processes. This review first briefly covers some historical perspective on the discovery of apoptotic cell death, the characteristic morphology that accompanies this process, and the numerous cell types and mediators with which programmed cell death is associated. The bulk of the review discusses our current understanding of the biochemical and molecular mechanisms by which apoptosis occurs. Finally, the potential for therapeutic uses of apoptosis is discussed, along with some comments on the physiological importance of programmed cell death and where the future lies for this quickly expanding and exciting field.