The construct of experiential avoidance has become more frequently used by clinical researchers. Experiential avoidance involves the unwillingness to remain in contact with private experiences such as painful thoughts and emotions and is often proposed to be critical to the development and maintenance of psychopathology. This review summarizes the empirical studies on experiential avoidance as a factor in the etiology of maladaptive behavior and its relationship to specific diagnostic categories. Although some of the current literature suggests that experiential avoidance may be implicated in various forms of psychopathology, a fundamental limitation of this research is the lack of theoretical integration and refinement with regard to operationalizing and assessing experiential avoidance. Future studies should attempt to understand the core processes involved in experiential avoidance better, and then clearly operationalize the construct and determine its incremental validity relative to other constructs. © 2007 Wiley Periodicals, Inc. J Clin Psychol 63: 871–890, 2007.