It means they have completed a training program after going to medical school, and they have taken certification examinations to determine their proficiency in a particular specialty of medicine. Generally in the United States, doctors go to medical school for 4 years. After medical school, they will then go on for further post-graduate training at a hospital. This is known as an internship/residency. The intership is their 1st year of training after medical school. After that 1st year, many hospitals consider the doctors to be in their residency. [This term comes from when doctors had to live on the hospital campus and literally be available day or night]. The length of a residency varies from 3 years up to 7 years depending on the specialty. During a doctor's internship & residency, they are employees of the hospital, and are [supposed to be] working under the supervision of an attending [senior] physician. In theory it sounds nice, but it doesn't always work in reality- especially in large municipal hospitals where the volume of patients can be overwhelming. After the doctor completes their accredited internship/residency, then they go out into the 'real' world and start practicing medicine- either in a group practice, a solo practice, or with a hospital. In many specialties, the doctor must complete 2 years of practice (called clinical practice) before becoming eligible to take their board certification exam. A board certification exam is a national exam, given to doctors in a specialty to test their knowledge and experience. If a doctor fails their board exam, they can retake it at a later date. Interestingly, they can continue to practice medicine in New York, without being board certified. As long as the doctor is licensed to practice medicine, they can practice anywhere they choose. A doctor does not need to be board certified to practice medicine in New York. As a patient seeking medical services, you should ask your doctor whether they are board certified, because this establishes the basic minimum standards that the doctor must meet before being able to say that they are 'board certified'. If your doctor has not passed his boards, then you know that there was some deficiency with his/her ability to pass the exam. Warning: There are good doctors who are not board certified who are practicing medicine in New York. Likewise, there are board certified doctors who may not be good doctors. Just because someone is board certified does not mean that they were not careless at a given point in time, nor does it mean that they are not responsible for injuries they may have caused you.