Intergroup threat is one catalyst that shifts us from out-group disregard to out-group hostility. We review recent inter-disciplinary research that explores the effects of intergroup threat on mind, brain, and behavior. A rapidly growing literature indicates that several types of intergroup threat — for example, realistic threats such as competition and resource scarcity — have significant effects on empathy toward, perceptual judgments of, and cognitive representations of out-group members. We also briefly consider the emerging research assessing biological markers of intergroup threat sensitivity. Converging evidence from psychology and neuroscience may help to elucidate the precise pathways by which intergroup threat creates subtle discrimination as well as overt conflict.