The ATP Tour is the world professional men's tennis circuit organized by the Association of Tennis Professionals. The second tier circuit is the ATP Challenger Tour, while the third tier is the ITF Men's Circuit.
The Tour is made up of tournaments of different international stature: the four Grand Slam tournaments, considered the most important in the world, the Australian Open, Wimbledon, Roland Garros and the US Open, the ATP Finals, the nine ATP World Tour Masters 1000 tournaments , the tournaments of the ATP World Tour 500 series, those of the ATP World Tour 250 series and those of the Challenger circuit. The lowest level of men's professional tournaments is that of the ITF Tour.
Of these tournaments, the Grand Slam and Tour Futures are organized by the ITF, the ATP Finals are jointly organized by the ATP and ITF, all others are organized by the ATP. All of these tournaments award points towards the ATP singles and doubles rankings.
The ATP publishes the rankings of professional players every week called the ATP Ranking, drawn up on the results of the last 52 weeks, used to draw up the entry lists and the seedings of the draws of all tournaments, both doubles and singles.
The points earned in each tournament will therefore be valid for 52 weeks, after which they will expire, with the exception of the points accumulated at the ATP Finals, which will be removed before the end-of-year event of the following season. In order to harmonize the classification with the new scoring system and the new calendar, at the beginning of 2009 all points have been doubled.