This chapter contains (1) an analysis of commonalities and differences in anxious solitude and social anxiety disorder, and a review of empirical investigations examining (2) correspondence among childhood anxious solitude and anxiety and mood diagnoses and (3) the relation between peer difficulties and temporal stability of anxious solitude and depressive symptoms. Findings support a diathesis-stress model in which anxious solitude forecasts symptoms of psychopathology primarily in the context of interpersonal stress. Additionally, evidence for individual and environmental factors which moderate risk for peer difficulties among anxious solitary children is reviewed. Implications for intervention are discussed.