Despite the importance of life satisfaction for health and well-being, there is a paucity of longitudinal studies tracking changes in life satisfaction in ethnic minority youth. In a sample of 674 Mexican-origin youth, the present research examined life satisfaction trajectories from middle (age 14) to late adolescence (age 17) and from late adolescence to young adulthood (age 21). On average, life satisfaction did not change significantly from age 14 to 17, and then decreased from age 17 to 21 (d = .30), perhaps reflecting difficulties transitioning into adult roles. Drawing on ecological systems theory, we examined both proximal (i.e., family) and distal (i.e., social-contextual) environmental factors (measured via self- and parent-reports) that may account for between-person variation in life satisfaction trajectories. Youth with more positive family environments in middle adolescence (age 14) had higher mean life satisfaction from middle adolescence to young adulthood (age 21). In contrast, youth with more negative family environments and who experienced greater economic hardship and more ethnic discrimination in middle adolescence (age 14) had lower life satisfaction during this period. Many of these factors also predicted change in life satisfaction from middle (age 14) to late adolescence (age 17), but not from late adolescence to young adulthood (age 21). This research extends the current understanding of life satisfaction during a critical developmental period in an understudied population. (PsycInfo Database Record (c) 2021 APA, all rights reserved).