Justine Henin (born 1 June 1982), formerly known as Justine Henin-Hardenne 2002–2007, is a professional Belgian tennis player. On 14 May 2008, Henin announced her immediate retirement from professional tennis. She was 25 years old and ranked World No. 1 at the time of her retirement. Billie Jean King has said that "pound for pound, Henin is the best tennis player of her generation." She announced her return to competitive tennis on September 22, 2009.

Henin won 41 WTA singles titles and more than US$19 million in prize money. Seven of those titles were Grand Slam singles titles, including four French Open titles, one Australian Open title, and two US Open titles. She also won the year-ending Sony Ericsson Championships twice and the singles gold medal at the 2004 Summer Olympics. Tennis experts cite her mental toughness, the completeness and variety of her game, her footspeed and footwork, and her one-handed backhand (which John McEnroe has described as the best single-handed backhand in the women's or men's game) as the principal reasons for her success.

At the 2007 French Open, Martina Navratilova said that "Henin's offense is just phenomenal ... it's sort of like we've got 'the female Federer', or maybe the guys have 'the male Justine Henin', because she is just head and shoulders above everyone else right now."