New research shows the critical impact of a child's "environment of relationships" on developing brain architecture during the first months and years of life. We have long known that interactions with parents, caregivers, and other adults are important in a child's life, but new evidence shows that these relationships actually shape brain circuits and lay the foundation for later developmental outcomes, from academic performance to mental health and interpersonal skills. However, many of our nation's policies, such as parental leave, child care, welfare work requirements, and child protection services fail to take into account the crucial importance of this environment of relationships and its impact on child well-being. This report summarizes the most current and reliable scientific research on the impact of relationships on all aspects of a child's development, and identifies ways to strengthen policies that affect those relationships in the early childhood years.