The DSM-IV Mood Disorders Field Trial addressed several issues concerning the relationship among major depression, dysthymia, recurrent brief depression, minor depression, and depressive personality disorder. The Mood Disorders Field Trial is a naturalistic, multisite study that investigated the diagnostic criteria for dysthymia, the reliability and validity of longitudinal course modifiers, the nosology of minor and recurrent brief depression, and the relationship between depressive personality disorder and dysthymia. Research on the nosology of chronic depressive disorders will, it is hoped, contribute to a better understanding of pathophysiology, etiology, and treatment. This article presents findings from the Field Trial as well as brief reviews of the other nine articles in this issue.