Adolescence is a period of rapid social changes that may have important implications for the ways adolescents think, feel, and behave in their close relationships. According to family systems theory, adolescents' attachment-related changes have the potential to spread throughout their family system, leading to coordinated changes in parents' and adolescents' attachment styles over time. The present study analyzed data from 205 adolescents (MageT1 = 14.0, SD = 0.9; 44% female, 56% male; 51% White, 33% African American, 3% Hispanic/Latino, 1% Asian American, 12% another race/ethnicity) and their parents (196 mothers, 105 fathers; median household incomeT1 = $100,000) who completed self-report measures of their general attachment styles annually for 5 years. Using a latent growth curve framework, we examined the extent of coordination among adolescents' and parents' long-term trajectories and shorter term fluctuations in attachment security. The results revealed a push-and-pull dynamic between mothers' and adolescents' long-term trajectories of attachment security. Mothers who reported higher initial levels of attachment anxiety tended to have adolescent children who reported higher initial levels of avoidance. Additionally, adolescents who increased in attachment avoidance over time tended to have mothers who increased in attachment anxiety. Mothers and fathers mirrored each other's patterns of attachment security as their children navigated their teenage years, reporting similar initial levels of attachment avoidance and synchronized shorter term fluctuations in attachment anxiety and avoidance across time. (PsycInfo Database Record (c) 2024 APA, all rights reserved).