Teacher experience has long been a central pillar of teacher workforce policies in U.S. school systems. The underlying assumption behind many of these policies is that experience promotes effectiveness, but is this really the case? What does existing evidence tell us about how, why, and for whom teacher experience matters? This policy brief distills the research on teacher experience into four general findings: (1) the effect of experience is most evident during the first few years of teaching; (2) the early-career experience effect varies by level of education and subject area; (3) inexperienced teachers are most likely to teach in high-poverty schools; and (4) the impact of experience differs for teachers in high- versus low-poverty schools. The brief concludes by discussing the implications of these findings for several key policy measures including teacher compensation, support and professional development, and the unequal distribution of teachers across schools.