<P> The ATP rankings are the Association of Tennis Professionals' (ATP) merit - based method 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 ATP - ranking points . 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 . </P> <P> Since 1973, 26 men have been ranked No. 1 by the ATP, of which 17 have been year - end No. 1 . The current world number one is Roger Federer . </P> <P> Since the introduction rankings the method used to calculate a player's ranking points has changed several times . As of 2011, the rankings are calculated by totaling the points a player wins in his best eighteen tournaments, subject to certain restrictions . For top players the counting tournaments are the four Grand Slam tournaments, the eight mandatory ATP World Tour Masters 1000 tournaments, the player's best four eligible ATP World Tour 500 series tournaments (the non-mandatory ATP Masters 1000 event in Monte Carlo may be substituted for one of these), and his best two results from ATP World Tour 250 series . Lower - ranked players who are not eligible for some or all of the top tournaments may include additional ATP 500 and ATP 250 events, and also ATP Challenger Series, and Futures Series tournaments . Players who qualify for the year - end ATP World Tour Finals also include any points gained at that tournament in their total, increasing the number of tournaments they may count to 19 . </P>

Who is ranked number 1 in mens tennis