Many educators have emphasized the importance of character for success in school and life. Yet our ability to measure character with accuracy and precision is limited, thereby curtailing the development of scientific knowledge about how adolescents develop character strengths and how these in turn influence important life outcomes. We propose a three-year project to address the need for practical, empirically-validated measures of character in adolescence: In the first year, we will develop multi-method batteries to assess five strengths of wide interest to educators and researchers: grit, self-control, prosocial purpose, actively open-minded thinking, and gratitude. Assessment modalities will include questionnaires, situational judgment tasks, performance tasks, and semi-structured interviews. In the second year, we will conduct a one-year longitudinal study of eighth graders, followed across their transition to high school, to establish empirical evidence of reliability and validity. In the third year, we will work with Character Lab leadership to promote wide use of these measures in research and educational practice.