This article reviews the observational, laboratory, and field experimental literatures on interventions for reducing prejudice. Our review places special emphasis on assessing the methodological rigor of existing research, calling attention to problems of design and measurement that threaten both internal and external validity. Of the hundreds of studies we examine, a small fraction speak convincingly to the questions of whether, why, and under what conditions a given type of intervention works. We conclude that the causal effects of many widespread prejudice-reduction interventions, such as workplace diversity training and media campaigns, remain unknown. Although some intergroup contact and cooperation interventions appear promising, a much more rigorous and broad-ranging empirical assessment of prejudice-reduction strategies is needed to determine what works.