From diagnostic entities to multidimensional concepts in psychiatry: Comorbid psychiatric disorders in Schizophrenia -- Comorbid psychiatric disorders in OCD: The Spectrum-Concept -- Phenomenology: Clinical presentation of OCS in patients with psychotic disorders (psychopathology, classification, diagnosis) -- Epidemiology: Dimensional overlap: Schizotypic OCD, schizo-obsessive disorder -- Associations of comorbid OCS with psychotic and affective symptoms and general functioning -- Neurobiology: The neurocognitive impact of comorbid OCS in schizophrenia -- GxE interactions in the pathogenesis of OCS in schizophrenia -- Neurophysiological and Neuroimaging results -- Effects of antipsychotic treatment on OCS -- Therapeutical interventions -- Augmentation and combination strategies -- Cognitive behavioural therapy -- Directions of further research.