Book excerpt: It has long been accepted that depressive disorders comprise a biologically-based type, the so-called 'endogenous' or 'melancholic' depression, and a residual set of depressive conditions resulting from social factors. The difficulty has been in distinguishing the melancholic type of depression on the basis of clinical features. This book describes the development of a behavioral sign-based approach, the CORE system, and demonstrates its superiority to previous symptom-based diagnostic systems for depression. The authors suggest that the psychomotor signs elicited may indicate the likely pathogenesis of melancholic depression, involving the basal ganglia and connections to the frontal cortex. This is therefore a challenging new account of the classification and neurobiology of depression, that is certain to interest all clinicians involved in the evaluation or treatment of such patients. The CORE measure itself is incorporated as an appendix.