Association of Tennis Professionals in the context of "1999 ATP Tour"

Andre Kirk Agassi (/ˈæɡəsi/ AG-ə-see; born April 29, 1970) is an American former professional tennis player. He was ranked as the world No. 1 in men's singles by the Association of Tennis Professionals (ATP) for 101 weeks, including as the year-end No. 1 in 1999. Agassi won 60 ATP Tour-level singles titles, including eight majors, completing the Career Grand Slam. He also won an Olympic gold medal, the 1990 ATP Tour World Championships, 17 Masters titles and was part of the winning United States Davis Cup teams in 1990, 1992 and 1995. Agassi is one of eight men in history to win the Career Grand Slam in singles, and one of three men to complete the career Golden Slam in singles.

A teenage phenomenon, Agassi contested multiple major finals before winning his first at the 1992 Wimbledon Championships. His ranking thereafter dropped afterward due to surgery, but he recovered and won the 1994 US Open and 1995 Australian Open to reach the world No. 1 ranking for the first time. He was then troubled by personal issues during the mid-to-late 1990s, and despite an Olympic gold medal at the 1996 Atlanta Olympics, Agassi's ranking declined to as low as No. 141 in 1997, prompting many to believe that his career among the elite was over. Following a rigorous training regimen, Agassi then enjoyed the most successful run of his career over the next several years. He returned to the world No. 1 position in 1999 after completing the Career Golden Slam at the French Open, and during this latter half of his career also claimed a US Open title and three Australian Open titles. Competing well into the 2000s, Agassi retired from the sport following the 2006 US Open.

The Grand Slam in tennis is the achievement of winning all four major championships in one discipline in a calendar year. In doubles, a Grand Slam may be achieved as a team or as an individual with different partners. Winning all four major championships consecutively but not within the same calendar year is referred to as a "non-calendar-year Grand Slam", while winning the four majors at any point during the course of a career is known as a "Career Grand Slam".

The term Grand Slam is also attributed to the Grand Slam tournaments, referred to as Grand Slams or Majors, and they are the world's four most important annual professional tennis tournaments. They offer the most ranking points, prize money, public and media attention, the greatest strength and size of the field and, in recent years, the longest matches for men (best of five sets, best of three for the women). The tournaments are overseen by the International Tennis Federation (ITF), rather than the separate men's and women's tour organizing bodies, the Association of Tennis Professionals (ATP) and Women's Tennis Association (WTA), but both the ATP and WTA award ranking points based on players' performances in them.

The Professional Squash Association, or simply the PSA, is the governing body for the men's and women's professional squash circuit. The body operates in a similar fashion to the ATP and the WTA for tennis. The PSA's highest professional level, the PSA Squash Tour involves over 250 tournaments annually around the world. Over 1,200 players from five continents and more than 60 countries are registered with the PSA. Rankings are updated weekly based on performances.

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 (known as ATP World Tour between January 2009 and December 2018) is the sole worldwide top-tier tennis tour for men organized by the Association of Tennis Professionals (ATP) founded in 1990 that replaced the earlier dual Grand Prix Circuit and WCT Circuit. The second-tier tour is the ATP Challenger Tour and the third-tier is the ITF Men's World Tennis Tour. The equivalent women's organisation is the WTA Tour.

The International Tennis Federation, abbreviated as ITF, is the governing body of world tennis, wheelchair tennis, and beach tennis. It was founded in 1913 as the International Lawn Tennis Federation by twelve national tennis associations. As of 2016, there are 211 national and six regional associations that make up the ITF's membership. In 2026 it will be renamed as World Tennis.

The ITF's governance responsibilities include maintaining and enforcing the rules of tennis, regulating international team competitions, promoting the game, and preserving the sport's integrity via anti-doping and anti-corruption programs. The ITF partners with the Association of Tennis Professionals (ATP) and the Women's Tennis Association (WTA) to govern professional tennis.