The hospital environment has changed dramatically over the last few decades. In more recent times, emergency departments and critical care units have evolved to identify and manage critically ill patients, allowing them to survive formerly fatal diseases. There is increasing pressure to reduce the length of stay in the hospital and to manage complex disorders in the outpatient setting. This transition has been driven not only by efforts to reduce costs but also by the availability of new outpatient technologies, such as imaging and percutaneous infusion catheters for long-term antibiotics or nutrition, minimally invasive surgical procedures, and evidence that outcomes often are improved by minimizing inpatient hospitalization. Hospitals now consist of multiple distinct levels of care, such as the emergency department, procedure rooms, overnight observation units, critical care units, and palliative care units, in addition to traditional medical beds. A consequence of this differentiation has been the emergence of new specialties such as emergency medicine, intensivists, hospitalists, and end-of-life care. Moreover, these systems frequently involve "handoffs" from the outpatient to the inpatient environment, from the critical care unit to a general medicine floor, and from the hospital to the outpatient environment. Clearly, one of the important challenges in internal medicine is to maintain continuity of care and information flow during these transitions, which threaten the traditional one-to-one relationship between patient and physician. In the current environment, teams of physicians, specialists, and other health care professionals often replace the personal interaction between doctor and patient. The patient can benefit greatly from effective collaboration among a number of health care professionals; however, it is the duty of the patient's principal or primary physician to provide cohesive guidance through an illness. To meet this challenge, the primary physician must be familiar with the techniques, skills, and objectives of specialist physicians and allied health professionals. The primary physician must ensure that the patient will benefit from scientific advances and from the expertise of specialists when they are needed while retaining responsibility for the major decisions concerning diagnosis and treatment.