The authors conducted a study to evaluate changes in judgmental biases (cost and probability biases) as potential mechanisms explaining the efficacy of cognitive-behavioral therapy (CBT) for social anxiety disorder (SAD). They analyzed data from 86 participants who received CBT for SAD and completed measures of social anxiety and judgmental biases at pre-, mid-, and post-treatment. Their results showed that reductions in judgmental biases statistically mediated treatment outcome and that CBT led to greater reductions in biases than a waitlist control. Additionally, probability bias at mid-treatment predicted social anxiety reduction after controlling for working alliance, a plausible rival mediator. The findings provide support for changes in probability bias as a mechanism of action in CBT for S