Definition: The Open Era of tennis began in 1968, when most world-class tournaments first allowed professional players as well as amateurs to enter. Prior to the Open Era, only amateurs could enter the world's most prestigious tournaments, including the Grand Slams, leaving many of the top players of the day out of the competition. The distinction between professionals and amateurs had long been artificial and unfair, because many amateurs were receiving substantial compensation under the table. Once the governing bodies of tennis saw the light and allowed open competition, almost all of the top players became professionals. The quality of the major tournaments, the popularity of tennis, and the prize money for the players all surged strongly in response to the new Open Era rules.