Many of the popular diagnostic, assessment, and treatment practices in psychology and psychiatry have been the subject of repeated criticism for their organization of mental disorders into finite categories, rather than broad dimensions. These criticisms are particularly relevant to the anxiety and mood disorders, including social anxiety disorder, major depressive disorder, and generalized anxiety disorder. The present study was designed to investigate the dimensional nature of social anxiety, a particular form of psychopathology characterized by significant comorbidity and heterogeneity, through the development of an assessment tool and subsequent evaluation of its psychometric properties. The study included: (1) the development of the initial item pool and review by an expert panel, (2) an initial study to investigate the factor structure of the item pool and develop provisional scales, and (3) a second study to cross-validate the scales and investigate their convergent and discriminant validity, test-retest reliability, and self-informant agreement. Together, the study resulted in a psychometrically-sound, dimensional measure of social anxiety features consisting of six scales: behavioral avoidance, physiological arousal and avoidance, functional impairment, anhedonia, thought avoidance, and coping with substances.