PROJECT SUMMARY Substance use in pregnancy, including illicit substances and alcohol, is a critical public health problem, affecting 1 in 10 pregnancies. Because of the opioid crisis, there were recent exponential increases in diagnoses of maternal opioid use disorder and neonatal opioid withdrawal syndrome. In parallel, the rate of infants entering foster care nationwide grew 25% from 2011 to 2017; infants now account for one fifth of annual foster placements. At present, infants are the fastest growing group entering foster care, most due to parental substance use. The rise of infants in the US foster system garnered public attention leading to recent federal policy changes that aimed to prevent foster placement where possible by connecting caregivers to treatment for substance use disorder and mitigating postnatal adverse outcomes by providing wrap-around services through Plans of Safe Care (POSC). However, state responses to changes in federal policy have been disjointed, and research to date remains unclear as to whether these policies achieved their stated goal or had unintended consequences such as exacerbating underlying racial disproportionality in the system. This study aims to evaluate child welfare policy interventions and local factors to improve the wellbeing of pregnant people with substance use disorder and their infants by: 1) conducting a rigorous analysis of state statutes, regulations, and guidance related to POSC and categorizing POSC components likely to influence the implementation of services (e.g., treatment, postnatal supports); 2) determining if state POSC policies were associated with reductions in infant foster placements and emergency department visits for injury from abuse and whether implementation of POSC was associated with changes to racial and ethnic disproportionality in infant foster placement; and 3) qualitatively investigating the contextual barriers and facilitators influencing the implementation of POSC and exploring elements of POSC implementation associated with improving or worsening racial and ethnic equity through interviews with key stakeholders (e.g., frontline case workers, judges, clinicians, policymakers).