Medical Assistants can be certified or registered health care workers who perform the administrative and clinical tasks that doctors are too busy to do on their own. They should not be confused with physician assistants.

Medical assistants must work under a physician's direct supervision when performing clinical duties delegated by the physician.  Some states allow medical assistants to perform more advanced procedures, such as giving injections or taking X-rays, after passing a test or taking a course.

Medical assistants perform many administrative duties, including answering telephones, greeting patients, updating and filing patients’ medical records, filling out insurance forms, handling correspondence, scheduling appointments, arranging for hospital admission and laboratory services, and handling billing and bookkeeping. Duties vary according to state law and include taking medical histories and recording vital signs, explaining treatment procedures to patients, preparing patients for examination, and assisting during diagnostic examinations. Medical assistants collect and prepare laboratory specimens or perform basic laboratory tests on the premises, dispose of contaminated supplies, and sterilize medical instruments. They instruct patients about medications and special diets, prepare and administer medications as directed, authorize drug refills as directed, telephone prescriptions to a pharmacy, draw blood, prepare patients for x-rays, take electrocardiograms, remove sutures, and change dressings. Last but not least they serve as direct link and communicator between patient and other health care professionals whenever there is a need. According to the United States Department of Labor job prospects for medical assistants are excellent since medical assisting is predicted to be one of the nation's fastest growing occupations through 2018.

Medical assistants have traditionally held jobs almost exclusively in ambulatory care centers, urgent care facilities, and clinics, but this is now changing. Medical assistants now find employment in both private and public hospitals, as well as inpatient and outpatient facilities.