Virtually everybody interested in improving the performance of schools concentrates on the importance of teacher quality. Yet policy recommendations related to teacher quality frequently do not incorporate existing evidence about performance. This paper reviews the various strands of research related to teacher quality including: the role of aggregate salaries, the supply of teachers with different characteristics, the relationship between teacher characteristics and student achievement, and direct estimates of the value-added of teachers. This evidence is then related to current policy initiatives as generally bounded by recommendations to tighten up on teacher qualifications and recommendations to loosen up on entry with stronger subsequent incentives.