We review a series of interrelated studies on the development of children residing in institutions (i.e., orphanages) in the Russian Federation or placed with families in the USA and the Russian Federation. These studies rely on a single population, and many potential parameters that typically vary in the literature are similar across studies. The conceptual focus is on the role of early caregiver–child interactions and environmental factors that influence those interactions in children’s development. Generally, children residing in institutions that provided minimal caregiver–child interactions displayed delayed physical, cognitive, and social-emotional development. Children and adolescents adopted from such institutions at 18 months of age or older had higher rates of behavioral and executive function problems, even many years after adoption. An intervention that improved the institutional environment by increasing the quality of caregiver–child interactions—without changes in nutrition, medical care, sanitation, and safety—led to substantial increases in the physical, cognitive, and social-emotional development of resident children with and without disabilities. Follow-up studies of children in this intervention who were subsequently placed with USA and Russian families revealed some longer-term benefits of the intervention. Implications are discussed for theoretical understanding of the role of early caregiver–child interactions in development as well as for practice and policy.