Apoptosis, or programmed cell death (PCD), is a physiological response that eliminates unwanted cells, an evolutionarily ancient process that is present in all multicellular organisms. Apoptosis is used during embryogenesis as a way to shape future adult forms (eg, limbs, fingers) or to suppress vestigial embryonic structures (eg, genital organ involution during mammalian sexual differentiation). By eliminating unwanted cells, PCD is an important tool that provides space for new cells during the process of cell renewal (41). In higher vertebrates, apoptosis is employed to eliminate self-reactive lymphocytes during differentiation and again at the termination of an immune response to remove antigen-specific lymphocytes (3). The advantage of apoptosis over necrosis is the lack of an inffammatory response after cell death. Indeed, apoptotic cells do not release their contents into the milieu but shrink and are phagocytosed by tissue macrophages or dendritic cells (42). Apoptosis is a continually occurring, tightly regulated process that maintains the homeostatic cellular balance in a normal animal. PCD is relatively rarely directly observed in healthy animals. This is because apoptotic cells are potent triggers for phagocytosis and thus are rapidly removed from the environment. Nevertheless, recent studies have revealed high levels of host cell apoptosis associated with several protozoan infections, particularly among cells of the immune system. In this review we address how protozoan infection triggers apoptosis and consider the consequences of dysregulated PCD for the parasite and the host.