Early care and education (ECE) evolved around two goals: allowing parents of young children to work (the purpose) and promoting early childhood development (the promise). An extensive body of research has examined how ECE promotes child development. A much sparser body of research has studied how ECE access affects families' economic and psychological well-being, particularly from a developmental perspective. These imbalanced literatures have created an incomplete picture of the role of ECE in developmental science, and this gap in knowledge limits the extent to which both the purpose and the promise of ECE can be fulfilled. In this article, we argue that developmental researchers should pay more attention to the parent and family outcomes, processes, and mechanisms that depend on stable, high-quality care (the purpose), and how these downstream cascades influence child development in the short and long term (the promise). While these issues are international, in this article, we focus on the development of and research on ECE in the United States to illustrate how the focus on both the purpose and promise of ECE could expand policies and research in the area. (author abstract)