The PIF ATP rankings are the Association of Tennis Professionals' (ATP) merit-based system for determining the rankings in men's tennis. The top-ranked player is the player who, over the previous 52 weeks, has garnered the most ranking points on the ATP Tour. Points are awarded based on how far a player advances in tournaments and the category of those tournaments. The ATP has used a computerized system for determining the rankings since August 23, 1973. Starting in 1979, an updated rankings list is released at the beginning of each week. Since 1973, 29 players have been ranked No. 1 by the ATP, of which 19 have been year-end No. 1.