Human mothers commonly receive help from others to support their children, an unusual reproductive system known as cooperative breeding. Because cooperative breeding is not a trait shared with other great apes, its emergence in the human lineage marks a significant departure in reproduction and parenting, which has far-reaching consequences for the life history, sociality, and demographic success of our species. This chapter first defines cooperative breeding and establishes those characteristics that distinguish humans from other cooperative breeders. To unravel the evolutionary puzzle of cooperative breeding, the benefits of helping to mothers and offspring, why helpers help, who helps, and what helpers do are then reviewed. The discussion then turns to the question of why humans become cooperative breeders. Because humans provide food, shelter, and protection not just to infants but also to juveniles, humans expand the range of helping behaviors beyond those observed in other cooperative breeders, which has implications for many other aspects of sociality. Cooperative breeding has much to offer as a framework for conceptualizing the cooperative nature of humans and to explain our derived life history of early weaning, high fertility, and the long developmental period during which juveniles benefit from both receiving and giving help.