Jack Brehm's psychological reactance theory (PRT) offers an explanation for how individuals respond to a threatened or eliminated freedom. Although the theory is not new, within the past decade PRT has emerged as a leading framework among health communication researchers. Researchers have used this theory to explain why some persuasive messages are ineffective with their intended audience. Attention is given to PRT's theoretical principles, measuring psychological reactance, message features associated with reactance, outcomes of reactance, and trait reactance as a segmentation variable.