The health care system in the United States has been less effective and more expensive than it needs to be, but the organizational and political will to address these shortcomings is beginning to emerge. These changes are particularly noticeable in primary care, at the heart of an improved health care system. The value of primary care turns on its comprehensiveness, which means that behavioral health care-health behavior change, mental health care, management of psychological symptoms and psychosocial distress, and attention to substance abuse-must be woven into the fabric of primary care practice. This integration is beginning to happen as psychologists and other behavioral health clinicians are incorporated as essential team members in the patient-centered medical home and other emerging models of primary care. This article introduces psychologists to the fundamental changes taking place in primary care and to the various roles that psychologists can play in the new health care system. We describe the extensive breadth and diversity of primary care by age, sex, setting, and type of clinical problem and the implications of this variety for the psychologist's role. This description is not simply a clinical exercise: Transformation of the primary care system also has policy, educational, and research dimensions. We describe how psychologists are essential to these functions as well.