Programmed cell death (PCD) occurs during the development of all animals that have been studied, but only recently has its molecular basis been discovered. In this review, we briefly consider some of the main events in the history of PCD in animal development. We then summarize what has been learned about the molecular mechanism of PCD and some of the intracellular proteins that control it. We next discuss the functions of PCD in development and how PCD is regulated during development by signals from other cells. Finally, we consider what the evolutionary origins of PCD may have been.