This document is a summary of the findings of an extensive review by the Education Commission of the States (ECS) of empirical research on the effectiveness of current approaches to licensing and certifying teachers. The research review focused on eight questions (and several subquestions) that are of particular interest and concern to policy and education leaders: (1) What kinds of pedagogical knowledge and practice are related to a teacher's effectiveness in promoting student achievement? (2) To what extent is the selectivity and rigor of teacher preparation programs associated with teaching quality and effectiveness? (3) What is the relationship between verbal ability and a teacher's effectiveness? (4) Is there empirical evidence for the validity and reliability of tests and methods frequently used in evaluating a teacher's effectiveness or quality? (5) To what extent is teaching experience associated with teaching quality and effectiveness? (6) To what extent does initial licensure and certification ensure a teacher's effectiveness? (7) What is the likely impact of raising teacher licensing and certification standards, specifically in raising cutoff scores on state-mandated tests? and (8) Is there empirical evidence of differences in the qualifications and performance of teachers prepared through traditional teacher education programs and those prepared through alternative certification programs? A glossary is included at the end of the document. [This document was also based upon research reviews by RMC Corporation.]