Why do grandparents invest so heavily in their grandchildren and what impact does this investment have on families? A multitude of factors influence the roles grandparents play in their families. Here, we present an interdisciplinary perspective of grandparenting incorporating theory and research from evolutionary biology, sociology and economics. Discriminative grandparental solicitude, biological relatedness and the impact of resource availability are three phenomena used to illustrate how these perspectives, within such a multi-level approach, add value by complementing not competing with each other. Changing demographics mean there is greater demand and opportunity for actively engaged grandparents to help their families, especially in times of need. Grandparents have been filling this emerging niche because in some societies the role of community and government never has, or increasingly cannot, meet the diverse needs of families. Built on an empirical foundation of descriptive and correlational research, grandparent research has rapidly entered a phase where the potential causal relationships between grandparents’ roles and family health, well-being and structure can be scrutinised. Together, these investigations are producing high-quality evidence that ultimately can support informed public policy and service delivery decisions. We finish by detailing two examples of such research efforts that highlight opportunities for future research.