Agoraphobia is a condition that most often occurs in the context of panic disorder and is characterized by intense fear or anxiety of places or situations in which escape might be difficult or help might not be available in the event of a panic attack or panic-like symptoms (APA, 2000). The purpose of this paper is to examine the behavioral mechanisms that may be responsible for the development and maintenance of the disorder, as well as how the disorder can be treated. In particular, the effective use in vivo exposure is described. Key words: In Vivo Exposure, Agoraphobia, Behavioral Treatments, Anxiety Disorders. ********** Agoraphobia is characterized by intense anxiety or fear of places or situations in which escape might be difficult or help might not be available in the event of a panic attack or panic-like symptoms (APA, 2000). These symptoms may include increased heart rate, sweating, trembling or shaking, shortness of breath, a feeling of choking, chest pain, nausea, dizziness, feelings of derealization or depersonalization, fear of going crazy, fear of dying, numbness or tingling sensations, or chills. The individual develops a fear of dying, losing control, or embarrassing themselves during these panic-like symptoms in a variety of situations such as driving, shopping, being in crowded places, traveling, standing in line, being alone, or attendance of meetings or social gatherings. Mowrer's two-factor theory (1960) proposes to explain the anxiety response based on the principles of both respondent and operant conditioning. Respondent conditioning is believed to have occurred with the pairing of a stimulus that evokes a fear response with stimulus by-products arising from strong bodily somatic sensations. Therefore, bodily sensations become conditioned responses triggered by high levels of private stimulation generated by anxiety and fear. When the individual is confronted with these triggers and the associated aversive emotions, the individual attempts to escape or avoid these triggers. The result may be a reduction in fear and distress and the individual learns through negative reinforcement that escape or avoidance of these cues reduces distress. Some debate exists on the completeness of the respondent conditioning mechanisms involved in the development of panic disorder (Bouton, Mineka, & Barlow, 2001). The debate in part centers on the role of selected cognitive appraisal processes in relation to fear conditioning. Nonetheless, behavioral researchers seem clear on the operant conditioning mechanism in the development of the agoraphobic response. Agoraphobia most often occurs in the context of panic disorder; however, it can become relatively independent of panic attacks (Craske & Barlow, 2001). An individual may not have had a panic response for some time, although the avoidance behaviors associated with agoraphobia remain. Not all persons who have experienced panic attacks or develop panic disorder go on to experience agoraphobia. There has been no evidence that age of onset or frequency of panic predicts an agoraphobic response, however, agoraphobia tends to develop in younger individuals. In a study by Bourden, Boyd, Rae, and Burns, (1988), 74% of the participants had developed agoraphobia before the age of 25. In addition, the likelihood that agoraphobia will develop increases as the length of panic increases (Craske & Barlow, 1988). Panic disorder with agoraphobia is diagnosed three times more often in women than in men (APA, 2000) and this gender difference increases as the severity of the agoraphobic response increases (Craske & Barlow, 1988). It can be challenging to differentiate agoraphobia from a specific phobia. A diagnosis of specific phobia must be considered if the avoidance is limited to one or only a few specific places or situations. Social phobia should be considered if the avoidance behaviors are limited to only social situations and fear of negative evaluation from others. …