There are two types of physicians: The M.D. (or medical doctor) or the D.O. (Doctor of Osteopathic medicine). They diagnose illnesses and prescribe and administer treatment to people suffering from injury or disease. As physicians, they are amongst the highest paid, and most respected of all professionals. They are also amongst the most rigorously trained. Four years of college, four years of medical school and three years of hospital internship and residency is the minimum requirement. Still more training is required for those who choose to specialize. The hours can be long and the paperwork required by health insurance companies and government agencies can be extensive. Physicians have to make what are, quite literally, life and death decisions. Yet, few experiences are more satisfying than easing someone's pain, fixing a broken body, or bringing a new baby into the world. Being an M.D. or a D.O. may be demanding but it can also be one of the most rewarding professions.