The past three decades have seen charter schools emerge as a prominent and controversial alternative to traditional public schools. This policy brief examines "Thirty Years of Charter Schools: What Does Lottery-Based Research Tell Us?" which summarizes 40 studies that have used lottery research designs to analyze how charter schools affect student outcomes. Most studies show that charter school attendance improves student academic achievement and boosts enrollment in a four-year college. But the evidence is mixed on gains elsewhere, including longer-term outcomes like college completion and earnings. Charter school practices vary substantially, with urban "high expectations, high support" schools generating the strongest improvement in student academic performance. Low-income, non-white students with lower baseline academic achievement tend to benefit the most from charter attendance.