At the end of the 19th century Emil Kraepelin dichotomized the so-called “endogenous psychoses” into dementia praecox (later schizophrenia) and manic-depressive insanity (later mood disorders). According to Kraepelin there are significant differences between the two groups regarding age at onset, phenomenology, and prognosis. But some years later Kraepelin himself recognized that there was a domain between the two groups showing a lot of overlaps and thus making a distinction impossible. Modern research confirmed this observation and opinion of Kraepelin: There are psychopathological syndromes showing characteristics of both mood and schizophrenic spectra. The overlap of the spectra gives rise to syndromes like schizoaffective disorders or acute and transient psychotic disorders having their own characteristics which differ from core schizophrenia or core mood disorders. Obviously there is a genetic determination of the overlap. The characteristics of syndromes created by the overlap of the spectra and the therapeutic consequences will be discussed.