Theories of romantic relationship development posit a progression of involvement and intensity with age, relationship duration, and experience in romantic relationships. Using the National Longitudinal Study of Adolescent Health, this study tests these propositions by considering relationship type and patterns of relationships over the course of adolescence and their influence on relationship formation in young adulthood. Results confirm recent theories of relationship progression and the findings of smaller-scale empirical studies. Moreover, the findings add depth to debates on racial differences in relationship formation and demonstrate the developmental currency of adolescent relationship experience for young-adult relationship formation. Rather than being trivial or fleeting, adolescent romantic relationships are an integral part of the social scaffolding on which young-adult romantic relationships rest.