Madison Keys (born February 17, 1995) is an American professional tennis player. She has been ranked as high as world No. 5 in women's singles by the WTA. Keys has won ten career singles titles, including the 2025 Australian Open, defeating two-time champion Aryna Sabalenka. She was also the runner-up at the 2017 US Open.

Keys was inspired to start playing tennis after watching Venus Williams at Wimbledon on TV. Keys turned professional on her 14th birthday, becoming one of the youngest players to win a WTA Tour-level match a few months later. Keys first entered the top 100 of the WTA rankings in 2013 at the age of 17. She had her first breakthrough at a major in early 2015 when she reached the semifinals of the Australian Open as a teenager. Keys debuted in the top 10 of the WTA rankings in 2016, becoming the first American woman to realize this milestone since Serena Williams 17 years earlier. She reached the US Open final in 2017, losing to friend Sloane Stephens. Following years of injury struggles and lower results, Keys won her first major title at the 2025 Australian Open, consecutively defeating world No. 2 Iga Świątek and world No. 1 Aryna Sabalenka.

Known for a fast serve and one of the most powerful forehands in the game, Keys has used her aggressive playing style to become one of the leaders of her generation of American tennis, alongside Stephens. She has had success on all surfaces, winning at least one title on each and having reached at least the quarterfinals of all four majors.

Keys was born on February 17, 1995, in Rock Island, one of the Quad Cities in northwestern Illinois. Her parents Rick and Christine are both attorneys, and her father was a Division III All-American college basketball player at Augustana College. She has an older sister named Sydney and two younger sisters named Montana and Hunter, none of whom play tennis. Keys' passion for tennis started at a young age. Her interest in the sport arose from watching Wimbledon on television when she was four years old. Keys asked her parents for a white tennis dress like the one Venus Williams was wearing, and they offered to get her one if she started playing tennis. Her father said that after this bargain, "All [Madison] did was try to hit balls into the next yard — home runs."

Keys started playing tennis at the Quad-City Tennis Club in Moline. She began taking lessons regularly at seven and began competing in tournaments at the age of nine. When she was ten years old, she moved to Florida with her mother and younger sisters so that she could train at the Evert Tennis Academy founded by John Evert and also partly run by his sister, International Tennis Hall of Famer Chris Evert. At first, John said that he "thought she was very athletic, a raw talent physically. She definitely needed to be cleaned up with her strokes." Keys noted that her game was very different when she was starting out at the academy compared to how it is as a pro, saying, "I didn't like groundstrokes, I didn't like long points that much, so I would just run into the net and try and volley." Nonetheless, Keys's coaches had high hopes for her. Chris said, "At 12 years old, she's pretty much an all-court player; she's not one-dimensional, which is pretty rare in this day and age."

When Keys was 12 years old, she went 23–2 in her girls 12s matches, including a perfect 19–0 in 2007. Her most notable title was a victory at the 12-and-under Junior Orange Bowl. At the age of 13, Keys began competing in 18-and-under ITF events. In January 2009, she won the Copa del Café, a high-level Grade 1 tournament in Costa Rica, to become the first American winner of the girls' event in its 26-year history. Later that year, her coach John Evert remarked that, "She's got weapons at a very young age. Most of the top players in the world have weapons, but it takes some time to develop them. Madison at the age of 14 can hit her serve or her forehand as big as most of the girls, and some of the top girls, on the pro tour."

As a 15-year-old, Keys played in just five ITF Junior Circuit events, instead opting to play in eight ITF Pro Circuit events over the same period. Her best result that year was winning both the singles and doubles titles at the Grade B1 Pan American Closed ITF Championships, which is the highest level of regional tournament on the junior tour. After the 2011 US Open, Keys moved to the pro tour full-time. She was ranked No. 16 in the ITF junior rankings at the time, a personal best. At this stage of her career, she was already 5' 10", serving at 115 miles per hour (185 km/h), and could hit strong forehand and backhand winners.

Keys turned pro in February 2009 on her 14th birthday. She made her WTA Tour debut a few months later at the Ponte Vedra Beach Championships, having played in only one previous professional tournament where she lost her only match. In her debut, she defeated world No. 81, Alla Kudryavtseva, in straight sets. At the age of 14 years and 48 days, she became the seventh-youngest player ever to win a WTA Tour-level match and the youngest since Martina Hingis in 1994. Top seed Nadia Petrova knocked Keys out of the tournament in the next round. Due to the tour's age restriction policy, she was unable to enter another WTA tournament that year. Nonetheless, Keys found another opportunity to play against the top professionals by participating in the World TeamTennis league as a member of the Philadelphia Freedoms. Still only 14 years old, she beat Serena Williams in a set to five games. Williams was ranked No. 2 in the world at the time and had just won Wimbledon earlier that month.