The Engagement, Perseverance, Optimism, Connectedness, and Happiness (EPOCH) Measure of Adolescent Well-Being (Kern, M. L., Benson, L., Steinberg, E. A., and Steinberg, L. [2016]. The EPOCH measure of adolescent well-being. Psychological Assessment, 28, 586-597) is a recently developed and validated scale to assess adolescent well-being and positive functioning. This measure includes five dimensions of developmental assets (i.e., EPOCH) that can foster adolescents’ well-being, physical health, and other social-emotional outcomes. Prior studies have tested measure equivalence across demographic, cultural, and language groups. The current study examined the validity of the EPOCH measure, using a national sample of adolescents from socioeconomically disadvantaged families ( n = 3444) in the United States. Consistent with theoretical expectations, confirmatory factor analyses supported the hypothesized first-order and second-order factor structure. The overall EPOCH scale and its subscales were also associated as expected with adolescents’ depression, anxiety, behavior problems, delinquency, school connectedness, and social skills. Findings provide empirical support for the EPOCH and its underlying multidimensional theory of adolescent well-being. Unexpectedly, the dimension of engagement was not found to be highly related to other dimensions, and its items had low factor loadings on the EPOCH construct in the current data. Implications of the study are described and directions for future research discussed.