More than 20 years into the implementation of public charter schools, the U.S. experience can inform policymakers and others about how to achieve the best possible results through charter school policies. This paper describes the history and current state of the charter school movement, presents a conceptual model of the charter school system, and reviews the extant research on charter school outcomes. The paper concludes with a discussion of the implications of the findings, reviewed for policymakers and researchers, and a list of remaining research topics in the field of charter school research.