Research has demonstrated the fluidity of racial self-identification and interviewer classification, but how they influence each other over time has not been systematically explored using national, longitudinal data. A typical theoretical prediction, consistent with theories of a “looking-glass self,” is that people calibrate their self-identification in accordance with how they are perceived by others. We examine the degree to which this and other symbolic-interactionist processes account for the dynamics of racial categorization among young adults in the United States. To do so, we deploy a conceptual framework focused on three key dimensions of variation—concordance, stability, and influence—that capture both inconsistency in racial categorization at a given point in time and fluidity in either measure of race over time. We find that while the standard looking-glass self-perspective accounts for the majority of racial fluidity, a substantial proportion of changes in both measures of race remain unexplained by existing theory.