Research Domain Criteria (RDoC), an initiative of the National Institute of Mental Health, is an explicit effort to break free from constraints of current diagnostic categories and to rebuild psychiatric taxonomy on new grounds. This chapter focuses on faulty brain circuits have led some to suspect RDoC of being a reductionistic enterprise. It explores the presumed reductionism of RDoC. The chapter argues that at least in principle, RDoC could enrich rather than impoverish clinical psychiatry. The RDoC's research program recognizes explicitly the role of high-level factors in the etiology of mental disorders, some of its advocates seem to derive from reductionist ontological thesis about mental disorders a reductionist epistemological thesis. The incorrect inference that consists of deducing epistemological reductionism from ontological reductionism could cause clinical psychiatry to be reduced to applied neurobehavioral neurosciences. The chapter concludes by demonstrating that despite its revolutionary potential for clinical psychiatry, RDoC could lead to the transformation of clinical psychiatry into an applied behavioral neuroscience.