In previous chapters of this book, it has become clear that grandparents are, as part of the human species’ typical childrearing practices (cooperative breeding), often highly involved in the lives of their grandchildren. The way this involvement may benefit the grandchild, however, is another question. If the involvement of grandparents increases child wellbeing as they interact, for instance, by teaching grandchildren to read, one could assume that grandparental involvement can truly improve child development. In this chapter, we review studies investigating whether grandparental presence has been associated with improved child survival in historical and traditional societies and whether grandparental investment correlates with child wellbeing in modern welfare states.