Stattin and Magnusson present prospective longitudinal data focused on the biological and psychosocial development of 466 girls from age 10 to 26. They are highly successful in taking a truly interactionist perspective of the adolescent and her environment, in the domains of self-concept, problem behavior, school achievement, sexuality, social relationships, work, family, and substance abuse. Detrimental effects of early maturation are found for social behavior and emotional states, but the effects, they suggest, are narrower in societies with stronger age segregation and broader in societies with less. The work reinforces the need for more cross-cultural comparative research.