Primary care doctors, such as general internists, family doctors, and general pediatricians, provide general care rather than focus on a narrow area of medicine. A major role of primary care doctors is to coordinate care for their patients. This coordination often requires that primary care doctors interact with other doctors who care for the same patients. Little is known about the number of other doctors that a primary care doctor may need to interact with. This information would be useful in developing models that serve to improve patient care. Coordination of care is a major focus of the patient-centered medical home, a model of care that some experts are currently promoting as a way to improve the quality of care in the United States.