Kim Antonie Lode Clijsters (Dutch pronunciation: [kɪm ˈklɛistərs] ; born 8 June 1983) is a Belgian former professional tennis player. She was ranked as the world No. 1 in women's singles by the Women's Tennis Association (WTA) for 20 weeks, and as the world No. 1 in women's doubles for 4 weeks, having held both rankings simultaneously in 2003. She won 41 singles titles and 11 doubles titles on the WTA Tour, including four singles majors and two doubles majors (both partnering Ai Sugiyama), as well as three singles titles at the Tour Finals.
Clijsters competed professionally from 1997 in an era in which her primary rivals were compatriot Justine Henin and Serena Williams. Coming from a country with little historical success in tennis, she established Belgium as a leading force in women's tennis alongside Henin, as the two of them led their country to their first Fed Cup crown in 2001 and were the top two players in the world in late 2003. Following defeats in all of her first four major singles finals, Clijsters finally won her first singles major at the 2005 US Open.
Plagued by injuries and having lost desire to compete, Clijsters retired from tennis in 2007 at the age of 23 to get married and have a daughter. She returned to the sport two years later and stunned the tennis world by winning the US Open as an unranked player in just her third tournament back. She defended the US Open title the following year and then won the Australian Open in 2011, becoming the first mother to be ranked world No. 1. Along with Margaret Court, she co-holds the record for most major singles titles won as a mother (with three), and was the first mother to win one since Evonne Goolagong Cawley in 1980. Clijsters retired again following the 2012 US Open. She had a second, short-lived comeback from 2020 to 2022.
Clijsters was born to athletic parents with backgrounds in professional soccer and gymnastics. She was renowned for her athleticism, which was highlighted by her ability to perform splits on court in the middle of points. She built the offensive side of her game around controlled aggression while also using her exceptional movement to become an elite defensive player. Clijsters was very popular and well-liked as a player, winning the Karen Krantzcke Sportsmanship Award eight times. She was inducted into the International Tennis Hall of Fame in 2017.
Kim Clijsters was born on 8 June 1983 in Bilzen, a small town in northeastern Belgium. She grew up with her younger sister Elke in the nearby town of Bree in the Flemish province of Limburg. Kim is the daughter of Lei Clijsters and Els Vandecaetsbeek, both of whom were accomplished athletes. Her mother Els was a Belgian national artistic gymnastics champion. Her father Lei was a professional soccer defender who played for a variety of clubs in the top-flight Belgian First Division, including KV Mechelen with whom he won the UEFA Cup Winners' Cup in 1988. He was also a member of the Belgium national soccer team, tallying 40 caps and competing in two World Cups. Clijsters credits her parents for giving her a footballer's legs and a gymnast's flexibility. She also attributes her success to the freedom they gave her when she was a young player, saying, "They've let me make my own decisions."
When Clijsters was five years old, her father built a clay tennis court at their home as a gift to his daughter to celebrate him winning the 1988 Gouden Schoen (player of the year in the Belgian First Division). Clijsters began playing tennis earlier that year after attending a lesson with her cousins and her uncle while her parents were away. From then on, she became fixated on the sport. She began playing with her sister at the Tennisdel club in Genk by the time she was seven. Her first coach Bart Van Kerckhoven recalled that she was extremely energetic and never wanted to leave the tennis court, adding that, "If the group before her did some sprints to finish off the session, Kim would join in. Then she put her heart and soul into her own training session, after which she joined the next group for their warm-up exercises."
At the age of nine, Clijsters began working with Benny Vanhoudt in the more distant town of Diest. Along with her sister, she trained for fifteen hours a week, including five hours of individual instruction, which Vanhoudt said was "an insane amount [of total hours]." She continued to train in Diest until she was twelve. During this time, she also first worked with Carl Maes and Wim Fissette, both of whom would coach Clijsters later in her professional career. When she was thirteen, Maes took over as her primary coach at the Flemish Tennis Association in Antwerp.
Clijsters had success at both the national and international levels at a very young age. In 1993, she won the 12-and-under division of the Belgian Junior Championships (the Coupe de Borman) in doubles with her future longtime rival Justine Henin. At the time, Clijsters was ten years old and Henin was eleven. A year later, she won the 12-and-under singles event at the same tournament. Clijsters continued to play alongside Henin, winning the doubles event at the 14-and-under European Junior Championships as well as the 14-and-under European Junior Team Championships for Belgium, both in 1996 and the latter of which also with Leslie Butkiewicz. Her first big international junior title came at Les Petits As, a high-level 14-and-under tournament. She defeated future top 25 players Iveta Benešová and Elena Bovina in the semifinals and final respectively.
Clijsters played two full seasons on the ITF Junior Circuit, the premier junior tour that is run by the International Tennis Federation (ITF). At the very end of 1997, she partnered with Zsófia Gubacsi to win her first ITF title in the doubles event at the Grade A Orange Bowl, one of the highest level junior tournaments. In 1998, Clijsters had her best year on the junior tour, finishing the season at career-high rankings of world No. 11 in singles and world No. 4 in doubles. She won two junior Grand Slam doubles titles, the French Open with Jelena Dokic and the US Open with Eva Dyrberg. She defeated her French Open partner Dokic in the US Open doubles final. In singles, she made it to the Wimbledon final, but finished runner-up to Katarina Srebotnik.
1997–99: Maiden WTA title, Newcomer of the Year
As a fourteen year old, Clijsters could only enter professional tournaments through qualifying since the WTA Tour's policy did not allow players her age to receive main draw wild cards. In August 1997, Clijsters qualified for her first main draw at her second career tournament on the lower-level ITF Women's Circuit, which was held in the Belgian coastal town of Koksijde. She won seven matches in total, including five in qualifying, to reach the quarterfinals. Clijsters did not enter another professional tournament until after her runner-up finish at the Wimbledon girls' singles event the following summer. Playing in Brussels in July 1998, she won both the singles and doubles events for her first career professional titles. Clijsters continued to excel at the ITF level, winning four more titles within the next year, two in both singles and doubles.
Clijsters began 1999 with a WTA singles ranking of No. 420 in the world. Around this time, Belgian women's tennis was beginning to flourish. Both Dominique Van Roost and Sabine Appelmans had been ranked in the top 20 within the previous two years, complementing the rise of Clijsters and Henin on the junior tour. This success helped lead to the revival of the only WTA tournament in Belgium, which was relaunched as the Flanders Women's Open in Antwerp after not being held in six years. Clijsters made her WTA debut at the tournament in May, entering the main draw as a lucky loser after losing in the final round of qualifying. She won her first career tour-level match against Miho Saeki and advanced to the quarterfinals, where she was defeated by top seed Sarah Pitkowski despite holding match points.