We introduce this special issue on the foundations and functions of adolescent thriving by summarizing the developmental systems theory-based, positive youth development (PYD) perspective. The PYD perspective frames much of contemporary research about health and positive development across the adolescent period and, more specifically, frames the 4-H Study of PYD, the data set from which the empirical work in this special issue is drawn. We discuss the different ways in which the articles in this special issue elucidate different facets of the PYD perspective. In addition, we summarize the implications of this research for future scholarship and for applications aimed at improving the life chances of diverse adolescents.