The charter school sector in the United States has grown steadily since the first charter school opened in 1992. As of the 2015–2016 school year, more than 6,800 charter schools served nearly 3 million students in forty states and the District of Columbia. Overall, research suggests that the average charter school performs about the same as nearby traditional public schools, but there is great variation in the effects of charter schools. Some charter schools are successful in boosting student achievement and others are not, which raises the question of what characteristics distinguish good charter schools from bad. This paper addresses this issue by summarizing the research on factors associated with successful charter schools. The research suggests that urban charter schools and charter schools primarily serving low-achieving and low-income students have the strongest positive impacts on student achievement. The policies most consistently found to be associated with positive charter school impacts include long school days or years, comprehensive behavioral policies with rewards and sanctions, and a mission that prioritizes boosting student achievement. In addition, moderately strong evidence suggests that high-dosage tutoring, frequent feedback and coaching for teachers, and policies promoting the use of data to guide teachers’ instructional practices are positively associated with charter schools’ achievement impacts.