Districts and states are targeting summer break -- the most substantial chunk of out-of-school time in the typical year -- as a prime opportunity to help students make progress with learning left unfinished due to the COVID-19 pandemic. Federal COVID relief funds will allow schools the freedom to offer programs as they never have before. But not all summer learning programs are created equal, and the pressing issue of unfinished learning makes it all the more important for providers to spend funds in a way that will benefit students the most. This research snapshot summarizes some of the most recent and relevant research on what makes summer learning programs effective.