Several years ago, Horvitz and Sulston demonstrated that it is the fate of 131 cells to die during development of the small nematode, Caenorhabditis elegans. The recognition that these particular cells are destined to die at exactly the same time in each and every worm suggested that the control and, perhaps, even the elements of this program were genetically determined. From these beginnings, the still-unfolding genetics of cell death has emerged. During the past 10 years, classical genetic approaches have identified loci in worms that either positively or negatively regulate cell death during development. Recently, some of the genes encoded by these loci have been cloned and sequenced. The results from these studies, coupled with experiments directed at identifying the events that regulate mammalian cell death, have led to the important observation that, in many instances, genes that control cell death in worms are conserved structurally and functionally between nematodes and vertebrates.