This first article, in a series of two, on the physiological approach of psychiatric semiology proposes to explore the place of physiology and clinical semiology in three systems of psychiatric classifications currently proposed in research: the Diagnostic and Statistical Manual of Mental Disorders (DSM), the Research Domain Criteria Project (RDoC), and the Hierarchical Taxonomy of Psychopathology project (HiTOP). For each of these systems will be presented the general principle, the link with physiology and semiology, and the main limitations. Physiology and clinical manifestation occupy a variable place and role in these three systems of psychiatric classifications. The DSM proposes a list of semiological criteria that are relevant to the clinical history of psychiatry, but the choice of these criteria and their organization remains guided by purely practical and nosographic issues with a very limited place for physiology. The RDoC project does not propose a list of semiological criteria. Its clinical and practical relevance is clearly questionable, but this project has the merit of emphasizing the importance of physiology in the medical approach of mental disorders. The HiTOP project does not in itself propose a list of semiological criteria, but proposes a hierarchical organizational framework of the nosography allowing to associate a set of signs and symptoms with supposed underlying psychopathological mechanisms. The challenge remains to coherently hang these psychopathological mechanisms to physiopathological mechanisms of mental disorders according to an integrative perspective of mental disorders.