Substance use disorder (SUDs) frequently co-occur with other forms of psychopathology, including externalizing and internalizing disorders. In my research, I study the phenotypic relationships among these forms of psychopathology and the shared genetic influences that give rise to these relationships. My goal is to integrate phenotypic classification with statistical genetics studies to improve gene discovery for SUDs and co-occurring forms of psychopathology and advance the development of precision medicine.