Primary care clinicians care for an extremely diverse range of patients, and they therefore have numerous opportunities to measure and act to improve the health of various populations. In order to take effective actions to improve the health of their patient populations, primary care clinicians must measure health. Strong population health metrics are characterized by their high validity, consistency, feasibility, and interpretability. Population health metrics should be applied longitudinally to obtain the most information from available data. Optimal population health metrics are actionable and facilitate the implementation of effective strategies to improve population health through administrative or clinical programs.