During summer vacation, many students lose knowledge and skills. By the end of summer, students perform, on average, one month behind where they left off in the spring. Participation in summer learning programs should mitigate learning loss and could even produce achievement gains. Indeed, educators and policymakers increasingly promote summer learning as a key strategy to improve the achievement of low-performing students. Rigorous studies have shown that strong summer programs can achieve several important goals: (1) reverse summer learning loss; (2) achieve learning gains; and (3) give low-performing students the chance to master material that they did not learn during the school year. The authors recommend that districts and other providers invest in staffing and planning for summer learning programs, actively incorporate practices that will help ensure the success of programs, and maximize the benefits of partnerships and a variety of funding sources. They also offer recommendations for policymakers and funders who are interested in supporting summer learning programs.