Many clinicians and researchers are convinced that there is an overlap between affective and schizophrenic spectra. In this book, an international team of experts discuss aspects of comorbidity, genetic models, clinical course, phenomenology and therapies. This is the first comprehensive overview of the schizoaffective spectra. Challenging cases presenting clinical and paraclinical features of both spectra are surprisingly numerous. Not only the phenomenology but also the course, outcome and treatment of such cases have their own characteristics. Recent research shows that the overlap also involves genetics and biological processes related to psychotic disorders. Within the overlap of affective and schizophrenic spectra it is possible to identify some groups of disorders having similar clinical and non-clinical features: the 'schizoaffective' group, 'Acute and Transient Psychotic Disorder' or 'Brief Psychosis', and other groups found in so-called 'Atypical Forms'.