The Early Growth and Development Study (EGDS) is a prospective adoption study of birth parents, adoptive parents, and adopted children (n = 561 adoptees). The original sample has been expanded to include siblings of the EGDS adoptees who were reared by the birth mother and assessed beginning at age 7 (n = 217 biological children), and additional siblings in both the birth and adoptive family homes, recruited when the adoptees were 8 – 15 years old (n = 823). The overall study aims are to examine how family, peer, and contextual processes affect child and adolescent adjustment, and to examine their interplay (mediation, moderation) with genetic influences. Adoptive and birth parents were originally recruited through adoption agencies located throughout the United States following the birth of a child. Assessments are ongoing and occurred in 9-month intervals until the adoptees turned 3 years of age, and in one- to two-year intervals thereafter through age 15. Data collection includes the following primary constructs: child temperament, behavior problems and mental health, peer relations, executive functioning and school performance, and health; birth and adoptive parent personality characteristics, mental health, health, context, substance use, parenting, and marital relations; and the prenatal environment. Findings highlight the power of the adoption design to detect environmental influences on child development and provide evidence of complex interactions and correlations between genetic, prenatal, and environmental influences on a range of child outcomes. The study sample, procedures, and an overview of findings are summarized and ongoing assessment activities are described.