Neighborhoods influence children's health, so it is important to have measures of children's neighborhood environments. Using the Child Opportunity Index 2.0, a composite metric of the neighborhood conditions that children experience today across the US, we present new evidence of vast geographic and racial/ethnic inequities in neighborhood conditions in the 100 largest metropolitan areas in the US. Child Opportunity Scores range from 20 in Fresno, California, to 83 in Madison, Wisconsin. However, more than 90 percent of the variation in neighborhood opportunity happens within metropolitan areas. In 35 percent of these areas the Child Opportunity Gap (the difference between Child Opportunity Scores in very low-and very high-opportunity neighborhoods) is higher than across the entire national neighborhood distribution. Nationally, the Child Opportunity Score for White children (73) is much higher than for Black (24) and Hispanic (33) children. To improve children's health and well-being, the health sector must move beyond a focus on treating disease or modifying individual behavior to a broader focus on neighborhood conditions. This will require the health sector to both implement place-based interventions and collaborate with other sectors such as housing to execute mobility-based interventions.A long tradition of social science research has examined how neighborhoods influence socioeconomic and health outcomes during the life course. 1 In the past decade increasingly strong evidence indicates that there has been a causal relationship between children's neighborhood environment and educational attainment, employment, income, and health outcomes. 2,3 In addition, a large body of research has documented high levels of racial residential segregation in US metropolitan areas and high levels of geographic concentration of both poverty and affluence. [4][5][6][7] Starting in the 1990s, groundbreaking work by George Galster and colleagues has connected these two research traditions, ar-guing that an unequal "geography of opportunity" in metropolitan areas-that is, differential access to neighborhood-based opportunityleads to inequities in outcomes by race and ethnicity. 8,9 Building on the geography of opportunity scholarship, [10][11][12][13] in 2014 we published the Child Opportunity Index to provide the child health field with a measure of children's neighborhood opportunity, which we defined as the context of neighborhood-based conditions and resources (for example, early childhood education, schools, availability of healthy food) that influence children's healthy development and long-term outcomes such as health and socioeconomic mobility. 14 Our goal was to facilitate analysis of the