Identity development is a highly salient task for adolescents, especially those from immigrant backgrounds, yet longitudinal research that tracks simultaneous change in ethnic identity and American identity over time has been limited. With a focus on 177 Asian American adolescents recruited from an emerging immigrant community, in the current study, we used hierarchical linear modeling and found that ethnic identity tends to remain fairly stable across the 4 years of high school, whereas American identity increases over time. When ethnic identity and American identity were examined simultaneously, consistent with existing research, ethnic identity was positively associated with positive relationships, high self-esteem, academic motivation, and lower levels of depression over time. Although American identity was not significantly associated with depression, positive links with relationships, self-esteem, and academic motivation were found. Both identities were interactively associated with academic motivation. Acculturative implications and the importance of considering the dual construction of ethnic identity and American identity in light of adolescent adjustment are discussed.