A Grand Slam title is a championships title won in one of the four tournaments that make up the Grand Slam.
These tournaments, the Australian Open, the French Open, the Wimbledon Championships, and the U.S. Open, are considered the strongest tournaments in the world. They can therefore be considered a scale for measuring the strength of a player or double. Tallying their can serve as a measurement of their strength, relative to their contemporaries. The all-time list of winners thus gives an indication of the strongest players ever.
* active players † Lenglen won the French Open singles six times, but on four of these occasions, the tournament was open only to French players.
[AO: Australian Open, FO: French Open, WB: Wimbledon, US: US Open]