Establishing similarities and differences in the endophenotypic signatures within schizophrenia and bipolar families will provide important insights for future genetic studies, and clarify concepts about common and distinct aspects of pathophysiology, potentially meaningful heterogeneity with disorders, and the clinical boundaries of the two most common psychotic disorders in adult psychiatry. This line of investigation will potentially impact our conceptualization of psychotic disorders, help us make critical strides to identify the pathophysiology of psychosis, and guide development of new specific treatments targeting particular deficits.