Swiss tennis player Roger Federer becomes the No. 1 ranked men's singles player, a position he will hold for a record 237 weeks.

Tennis is a racket sport that is played either individually against a single opponent (singles) or between two teams of two players each (doubles). Each player uses a tennis racket strung with a cord to strike a hollow rubber ball covered with felt over or around a net and into the opponent's court. The object is to manoeuvre the ball in such a way that the opponent is not able to play a valid return. If a player is unable to return the ball successfully, the opponent scores a point.

Roger Federer is a Swiss former professional tennis player. He was ranked as the world No. 1 in men's singles by the Association of Tennis Professionals (ATP) for 310 weeks, including a record 237 consecutive weeks, and finished as the year-end No. 1 five times. Federer won 103 singles titles on the ATP Tour, the second most since the start of the Open Era in 1968, including 20 major men's singles titles and six year-end championships.

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.

The ATP Tour is the modern top-level men's professional tennis circuit. It was introduced in 1990 and it's administered by the Association of Tennis Professionals (ATP). All the records listed here are only for the players who played most of their careers on the ATP Tour and they're based on official ATP data. The names of active players appear in boldface. However, no boldface is used in lists exclusively for active players.