Data from the 2007 National Survey of Children's Health are used to develop an index of positive child well-being that has several innovative and important characteristics. It distinguishes child well-being from contexts of child development; it is built with rich micro-data (rather than population-level macro-data) to create unique measures of well-being for individual children; and it focuses on positive, rather than negative, aspects of development. These data can be aggregated to provide a perspective on the proportions of children in the population who are doing well on all, some, or no developmental domains. Based on child development theory and research, the index is constructed within a framework of four conceptually distinct developmental domains, each of which is comprised of three sub-domains. The index distinguishes among children in predicted directions, by poverty level and parental education. White children tend to do better than Hispanic or black children in all domains, though neither minority subgroup is consistently better or worse off than the other subgroup. Girls score slightly higher than boys on the index. About three in four children score positively on three or four domains. The index provides a composite, multidimensional view of positive child well-being that can be useful to researchers and policy analysts, and which addresses some weaknesses of other similar indices.