There are dozens of different medical specialty boards that certify doctors in different specialties and sub-specialties, ranging from internal medicine and psychiatry to urology, plastic surgery and ophthalmology. Many doctors have earned board certification in more than one specialty. In addition, there are many cases of people who have earned a doctorate in one field and gone on to earn one in another field.

Becoming a Doctor

To become any kind of medical doctor, a student must earn a bachelor’s degree and attend an accredited medical school to earn an M.D. or a DO. After med school, there are several more years of further training. This training, called a residency, typically takes place in a clinical environment like a hospital. It prepares doctors to work with patients and pursue a particular kind medical practice.

Residency and Specialty Training

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During a doctor's residency, she trains in one of the many specialties and becomes eligible to seek medical board certification. However, some doctors seek training in dual specialties, such as internal medicine and dermatology, internal medicine and psychiatry, or emergency medicine and family medicine. This dual training is often sponsored by the medical boards themselves. In some cases it takes less time than if the specialties had been pursued individually.

Subspecialty Training

To earn board certification in a subspecialty, a doctor must first become certified in the general specialty. Some programs train in dual subspecialties. For instance, there are more programs that prepare doctors for board certification in both hematology and oncology than either subspecialty on its own. Another popular dual sub-specialty combination, pursued by internists, is pulmonary disease and critical care medicine.

Multiple Disciplines

In addition to training in different medical specialties, there are also many cases of people who have earned doctorates in different fields, although they don’t always use the title “doctor.” A lawyer, for example, has gone to law school and earned a Juris Doctor. There are many lawyers who also have earned MDs, and several universities offer joint MD/JD programs. In addition, medical doctors who are engaged primarily in research may earn doctorates in fields such as chemistry and biology. Again, several universities offer joint MD/Ph.D. programs.