A Coroner is an official person who investigates and certifies deaths. Surprisingly, in the U.S., very few Coroners have any extensive medical training. They obviously have some basic knowledge, but often lack a formal medical education. Some Coroners do have medical training, but the vast majority do not. A Medical Examiner (ME) is a physician/official who works with law enforcement officers to determine cause and manner of death. In some countries, however, there is no difference and the terms are used interchangeablly. Even in the U.S. this is sometimes the case even if it is technically incorrect.

A medical examiner is generally required in larger populated areas. Some medical examiners cover several counties at one time, while coroners are generally specific to their one county. Coroners also aren't usually expected to testify in court cases. Medical examiners have their autopsy reports and other reports called in for evidence for homicides and traffic fatalities regularly. Another thing is coroners are generally elected or appointed to the position, which as Andy pointed out, makes it quite possible that someone could hold that position who has little to no medical experience or knowledge. Coroners used to be the funeral home directors in small towns that only had the one funeral home. One little side note...there is an organization of coroners that exists now with a code, bylaws, etc. But it's possible that people who are looking into geneology several generations back won't be able to find anything more than a death certificate for their family members, because there wasn't anything in place that passed coroner's records from one to the next. So if Dr. Smith died in 1932, it's quite probable that his family may not have maintained his files and any reports are no longer available. However, with a Medical Examiner, everything is (or should be) centrally kept, so that the doctor doesn't have "their own personal" files. If they quit or get replaced, they don't take the files with them. If they are needed at a later date, the doctor can get a copy of the original file, but that file doesn't leave the office (or it shouldn't anyway!).