With decades of evidence to support early childhood development (ECD) programs and policies, investment in ECD has expanded worldwide. Currently, over 70 nations have national ECD legislation, the majority in the last 20 years. However, with these increased investments comes evidence that the capacity of policy systems to support ECD-across health, education, social protection, and other sectors-is weak, with unfulfilled developmental potential a serious consequence within and across countries. This report aims to develop a research agenda on the systems-level factors-at national, subnational, and local or municipal levels-that may enable or constrain program site-level implementation. Two types of scale-"small to bigger" and "big to better"-are described, as well as the specific challenges of these processes in the field of ECD. Systems factors are reviewed at the three levels, with implications of each for measurement. Finally, methodological challenges and directions are discussed with the aim of informing a research agenda to support national policy progress in early childhood development. how human ecosystems can be changed to improve development, health, and well-being from conception to young adulthood in low-and middle-income countries. Particular interests pertain to how an individual's neurobiology interacts with contexts; the mechanisms through which interventions effect change; how stress physiology mediates/moderates intervention effectiveness; how changes in neurobiological markers inform questions of dose-response; and advancing tools to meaningfully and validly measure contexts, processes, and outcomes. In her capacity at Global TIES, Alice is working on multiple research projects in several low-, middle-, and conflict-affected countries, and across a variety of topics including early language development in pre-school children; home visiting, parenting, and early development; and implementation research to support scale and quality in early childhood development services.