Social phobia is maintained in part by cognitive biases concerning the probability and cost of negative social events. More specifically, individuals with social phobia tend to believe that negative social events are extremely likely to occur, and that if such events were to happen, the consequences would be awful or unbearable. The aim of the present review is to critically evaluate research on the nature and specificity of probability and cost biases in social phobia. Changes in probability and cost estimates during treatment and their relationship to treatment outcome are detailed. The review concludes with a discussion of how current cognitive behavioral interventions target these biases. Directions for future research are proposed.Keywords: social phobia; cognitive biases; cognitive behavioral treatment; review T heoretical models of social phobia (e.g., Glark 8c Wells, 1995; Rapee 8c Heimberg, 1997) emphasize the importance of biased cognitive processing in the development and maintenance of anxiety disorders. Indeed, it is thought that most fears are driven by faulty appraisals concerning the expectation or anticipation of potential future harm (e.g.. Beck, Emery, 8c Greenberg, 1985). Garr (1974) proposed that these perceptions of threat are composed of estimates of the probability of the event (i.e., the likelihood a given event will occur) and the cost of the event (i.e., the negative consequences associated with the event).Several theorists (e.g.. Beck,. 1976; Rapee 8c Heimberg, 1997) have identified mechanisms by which probability and cost biases may exert their influence. Social phobia is characterized by social fears-concerns about social embarrassment, humiliation, and subsequent rejection by others (American Psychiatric Association, 2000). Beck ( 1976) suggested that cognitive biases exacerbate and perpetuate these social fears via biased processing of social information. Specifically, overestimates of the probability and cost of negative social events result in the perception of social situations as dangerous. As a result, individuals with such fears tend to be hypervigilant to cues of social rejection. Individuals with social phobia often attend to internal cues that may elicit social disapproval (e.g., sweating, blushing), thereby resulting in a failure to encode information from © the external environment (e.g., Rapee & Heimberg, 1997). As such, biased accounts of social interactions (e.g.,"I was nervous and sweating so the speech must have gone poorly") are encoded into memory. This biased information processing results in inflated estimates of the probability of negative social events, as past social encounters are viewed as failures. It also creates exaggerated cost estimates, as individuals with social phobia interpret negative social events catastrophically. In short, probability and cost biases are believed to result in greater availability of social threat information in memory, increased attentiveness to social threat cues, and inflated estimates of the probability and cost of negativ...