Organization known as the Mafia or La Cosa Nostra began in Sicily
The job descriptions between the Mob and the Mafia may differ, but unfortunately for stool pigeons, squealers and other defectors, the results are generally the same. In the broadest sense of the terms, the Mafia can safely be described as a mob, but the Mob is not always associated with the true Mafia.
The original crime organization known as the Mafia or La Cosa Nostra began in Sicily, Italy, and membership is strictly limited to native Sicilians. The Mob has no such restrictions, which is why notable non-Sicilian gangsters such as Al Capone and Meyer Lansky could be considered mobsters, but not members of the official Italian Mafia.
Besides Sicilian heritage, another difference between the Mob and the Mafia is organization. The original Mafia created a very specific chain of succession, which some organized crime experts suggest was inspired by the Roman Catholic Church’s governing system. Rank-and-file members of the Mafia would have to work their way through the ranks in order to earn more respect from their superiors and gain more power within the organization. A mob, on the other hand, may not have a very well-established hierarchy. Leadership in a mob could change in an instant through sheer force or assassination.