The gold standard psychological treatment for social anxiety disorder (SAD), one of the most common anxiety disorders, is cognitive-behavioural therapy (CBT), incorporating cognitive restructuring to target maladaptive beliefs thought to maintain SAD. Recent evidence suggests that mindfulness- and acceptance-based approaches, emphasizing nonjudgmental awareness without active pursuit of cognitive change, may also be effective. The goal of the current study was to examine the mechanisms by which each cognitive approach affects symptoms. Eighty-seven adults with elevated social anxiety were randomized to receive training in one of the strategies or to a control condition in which participants completed assessments only. Participants self-reported similar decreases in symptoms after 1 week of practice, and these improvements were mediated by increases in decentering and decreases in maladaptive beliefs across condition. These results suggest greater overlap between modalities than theory might predict. Implications for clinical practice, including brief treatments and the role of assessment, are reviewed.