Youths who are negatively affected by social determinants of health suffer adverse effects like increased risks of chronic health conditions and mental health issues. Part 1 of this series describes many underserved communities and the various ways their status affects their health. Members of these vulnerable communities include foster children, runaway youths, immigrants, Black, Latinx, Native American, and other children from minority racial groups, LGBTQ+ youths, and children living in poverty. This collection describes the challenges faced by each of these populations and how that adversity shapes their present and future health.