We examine the mobility of individuals in the United States based on equivalent family income-that is, total income of all family members adjusted for family size according to the equivalence scale implicit in the U.S. poverty line. Our analysis, which tracks movements across quintiles, centers on four questions: How much movement is there across the family income distribution? How has this mobility changed over time? To what extent are the movements attributable to factors related to changes in family composition versus events in the labor markets? In light of major socioeconomic changes occurring in the quarter-century under study, have the determinants of mobility changed over time? Our findings indicate that mobility rates in the 1980s differed little from those in the 1970s. However, individuals in families headed by a young person or a person without a college education were less likely to experience upward mobility in the 1980s than in the 1970s.