Primary care physicians have assumed an increasingly important role in US outpatient mental health care. They are providing an increasing volume of outpatient mental health services, prescribing a growing number and variety of psychotropic medications, and treating patients with a broader array of mental health conditions. These trends, which run counter to a general trend toward specialization and subspecialization within US health care, place new strains on the clinical competencies of primary care physicians. They also underscore the importance of implementing more effective models of collaboration between primary care physicians and mental health specialists. Several elements of the Affordable Care Act provide options for financing and organizing the delivery of integrated general medical and behavioral services. Such integrated services have the potential to improve access and quality of outpatient mental health care for a range of psychiatric disorders. Because people with severe and persisting mental disorders commonly require a higher-level medical expertise than is readily available within primary care as well as a complex array of social services, separate specialized mental health will likely continue to play a vitally important role in caring for this population.