Part I. Definitional tensions -- Five criteria for an improved taxonomy of mental disorders / Robert E. Kendell -- Defining clinically significant psychopathology with epidemiologic data / Darrel A. Regier and William E. Narrrow -- Why requiring clinical significance does not solve epidemiology's and DSM's validity problem : response to Regier and Narrow / Jerome C. Wakefield and Robert L. Spitzer -- Psychometric perspectives on comorbidity / Robert F. Krueger -- Part II. Imaging psychopathology -- Toward a neuroanatomical understanding of psychiatric illness : the role of functional imaging / Jane Epstein [and others] -- Neuroimaging studies of mood disorders / Wayne C. Drevets -- Genetic neuroimaging : helping to define phenotypes in affective disorders / Kelly N. Botteron -- Part III. Longitudinal studies -- Psychopathology and the life course / Stephen L. Buka and Stephen E. Gilman -- Detectiing longitudinal patterns of alcohol use / John E. Helzer and John S. Searles -- Empirically based assessment and taxonomy across the life span / Thomas M. Achenbach -- ADHD comorbidity findings from the MTA study : new diagnostic subtypes and their optimal treatments / Peter S. Jensen and Members of the MTA Cooperative Group -- Part IV. Exploring alternatives -- Implications of genetic epidemiology for classification / Kathleen R. Merikangas -- Importance of phenotype definition in genetic studies of child psychopathology / James J. Hudziak -- Defining genetically meaningful classes of psychopathology / Stephen V. Faraone -- Schizotaxia and the prevention of schizophrenia / Ming T. Tsuang.