This resource gives an overview and non-technical introduction to randomized evaluations. Randomized evaluations can be used to measure impact in policy research: to date, J-PAL affiliated researchers have conducted more than 1,100 randomized evaluations studying policies in ten thematic sectors in more than 90 countries. This resource highlights work from a variety of contexts, including studies on youth unemployment in Chicago, a subsidized rice program in Indonesia, and a conditional cash transfer in Mexico. It includes guidance on when randomized evaluations can be most useful, and also discusses when they might not be the right choice as an evaluation method.