We introduce the EPOCH Measure of Adolescent Well-Being, which assesses 5 positive psychological characteristics (Engagement, Perseverance, Optimism, Connectedness, and Happiness) that might foster well-being, physical health, and other positive outcomes in adulthood. To create the measure, a pool of 60 items was compiled, and a series of 10 studies with 4,480 adolescents (age 10-18) from the United States and Australia were used to develop and test the measure, including the factor structure, internal and test-retest reliability, and convergent, discriminant, and predictive validity. The final 20-item measure demonstrated adequate psychometric properties, although additional studies are needed to further validate the measure, extend to other population groups, and examine the extent to which it predicts long-term outcomes. As a brief multidimensional measure, the EPOCH measure contributes to the empirical testing and application of well-being theory, and offers a valuable addition to batteries designed to assess adolescent positive psychological functioning. (PsycINFO Database Record