Interpersonal approaches to depression are surveyed; it is suggested that interpersonal inhibition, as opposed to interpersonal excess, has been underemphasized as an antecedent of depression. It is proposed that shyness is a vulnerability factor for depressive symptoms in the absence but not in the presence of social support and that loneliness mediates the relation between shyness and depressive symptom increases. Undergraduates (N = 172) reported on their levels of shyness, social support, loneliness, positive and negative affect, and depressive symptoms, and returned 5 weeks later to complete a similar set of assessments. Results supported hypotheses. Participants who were shy and unsupported were likely to experience increases in depressive symptoms and decreases in positive affect, whereas other students were not. This effect was partially mediated by increases in loneliness and was specific to depressive symptoms and low positive affect; it did not apply to negative affect.