General Medicine
internists do much of their work in hospitals. Formerly, many internists were not subspecialized and would see any complex nonsurgical problem; this style of practice has become much less common.

In modern urban practice, most internists are subspecialists: that is, they generally limit their medical practice to problems of one organ system or to one particular area of medical knowledge.
                           For example, gastroenterologists and nephrologists specialize respectively in diseases of the gut and the kidneys. Internists have a lengthy clinical and scientific training in their areas of medical interest, and have special expertise in the use of prescription drugs or other medical therapies (as opposed to surgery). While the name, "Internal Medicine," may suggest that internists only treat problems of internal organs, this is not the case. Internists are trained to treat patients as whole people, not as mere organ systems.  
Subspecialties of internal medicine
    
In the United States, there are two organizations responsible for certification of subspecialists within the field, the American Board of Internal Medicine, and the American Osteopathic Board of Internal Medicine.
The following are the subspecialties recognized by the American Board of Internal Medicine.