In education, teacher experience is probably "the" key factor in personnel policies that affect current employees: it is a cornerstone of traditional single-salary schedules; it drives teacher transfer policies that prioritize seniority; and it is commonly considered a major source of inequity across schools and, therefore, a target for redistribution. The underlying assumption is that experience promotes effectiveness. Is this really the case? Do students attain higher levels of achievement when taught by more experienced teachers? What is the relationship between teacher experience and teacher productivity? Over 40 years of teacher productivity research suggests that the simple assumption that "more is better" requires greater nuance; experience effects are complex and depend on a number of factors. Recent evidence from CALDER (National Center for Analysis of Longitudinal Data in Education Research) studies using rich state datasets provides new insight into the effects of teacher experience. Several key findings emerge, some confirming previous understandings and others raising new questions. These findings have important policy implications. This paper offers three recommendations: (1) Frontload experience-based compensation; (2) Implement evaluation, professional development, compensation, and dismissal policies that encourage ongoing effectiveness among veteran teachers; and (3) Look beyond policies to distribute inexperienced teachers evenly across high- and low-poverty schools, and identify retention strategies to increase returns to teacher experience in high-poverty schools. (Contains 10 notes and 4 figures.)