The Association of Tennis Professionals publishes weekly rankings of men's singles players and doubles pairs based on a point system that awards points for players' performance in tournaments contested during the previous 52 weeks. Each player receives points for his performance in four Grand Slam events, eight ATP World Tour Masters 1000 tournaments and his six best other ATP-sponsored tournaments during the previous 52 weeks. The ATP ranks over 1,500 singles players and doubles pairs each week.
The four Grand Slam tournaments—the Australian Open, the French Open, Wimbledon and the U.S. Open—are the most important for rankings purposes. Winners of a Grand Slam tournament receive 2,000 ratings points and runners-up receive 1,200. ATP Masters 1000, 500 Series and 250 Series events are so named because of the number of points awarded to the winners. A quarterfinal or semifinal appearance in a Grand Slam earns a player more points than winning a 240 Series tournament.
Because the ATP rankings cover the previous 52 weeks of play, each player needs to defend his ranking by finishing at least as well in a tournament as he did the previous year. If a player wins a Grand Slam event and then finishes as the runner-up the following year, he may drop in the rankings, because his previous winning performance is no longer counted. However, the ATP may grants an exception that allows a player to keep his ranking while injuries prevent him from playing in tour events.