Teacher evaluation systems are designed to measure the quality of instruction and contributions of teachers to the school learning environment. This entry covers the policy relevance of these systems in the United States with a focus on two important types of component measures used in many teacher evaluation systems—(1) those based on teacher practices and (2) those based on student achievement growth. It also discusses other measures, methods of summarizing results across these different component measures to obtain final evaluation scores and the future of teacher evaluation systems.