The delineation between amateur and professional sports is much clearer in some sports than in others. No one would confuse the regulations and players in high school basketball with those of the professional league. However, in tennis these lines are a bit more blurred, especially since the open era of tennis took hold in the late 1960s.
Prior to that time, amateur and professional competition were kept separate. Players were either professional champs or they were amateur champs . All this changed when that larger tournaments began allowing both types of players to compete in the same event. The idea was to let players to make a living from the sport while elevating the level of the game. Today almost all non-collegiate tournaments are open, as designated by the names of the events, like the US Open and the Australian Open.
The very first official open tournament was held in England at the West Hants Club. It was played on April 28, 1968. A month later, french open tennis followed suit. On May 27, 1968 the first Grand slam event to allow both professional and amateur competitors was held at Roland Garros. After the French Open led the way, the other Grand Slam events quickly became open tournaments as did much of the rest of the tennis circuit.