Employing the Integrated Public Use Microdata Series of the University of Minnesota, we chronicle the changing timing and duration of transitions to adulthood in the twentieth century. Successive generations of young Americans reinvented the transition to adulthood to accommodate shifts in the economy and the American state. The patterned choices of young people delineate three eras of social history in the twentieth century: the era of reciprocity (1900–1950), the era of dependence (1950–70s), and the era of autonomy (1970s-2000). We also explain why African Americans differed from the general trend; they developed distinctive transitions to adulthood in response to persistent inequality.