The process of economic development is demographically disruptive. It alters the structure and nature of relationships among family members and how families are connected through social, cultural, economic, and political networks. Conversely, demographic change shapes development. Empirical population science that addresses these complexities is critical to ensure that development leads to sustained, equitable improvement in welfare, including health and wellbeing. PSTC scholarship in this area is distinctive in its disciplinary and geographic breadth, as well as its diverse methodologies, ranging from local ethnographies to macroeconomic world region comparisons.