Psychiatric disorders and drug and alcohol use disorders commonly co-occur. A growing literature has documented the epidemiology and effects on the course of illness of comorbid psychiatric and substance use disorders (SUDs). Advances in treatment of co-occurring illnesses have progressed more slowly. The current article reviews recent developments in the diagnosis and treatment of co-occurring psychiatric disorders and SUDs with particular focus on psychotic disorders, affective disorders, anxiety disorders, personality disorders, and attention-deficit/hyperactivity disorder. Current treatment options and implications for future research are highlighted.