Forests and trees do indeed hold a lot of promise: Protecting and restoring the world’s forests, along with other land-oriented solutions, could deliver a third of the emissions reduction needed to keep global warming below 2 degrees Celsius by 2030 as agreed under the U.N. Paris Agreement. Unfortunately, forest conservation and reforestation at the necessary scale takes more than casting a magic spell. It is a big and complicated challenge. For more than a decade, REDD+ (Reducing Emissions from Deforestation and forest Degradation) has been expected to provide at least part of the solution. Yet, despite the initial excitement over implementation of REDD+ initiatives at national, subnational and local scales, evidence on how, when and under what conditions REDD+ works best is scarce.