2009 US Open (tennis)

The 2009 US Open was a Grand Slam tennis tournament played at the USTA Billie Jean King National Tennis Center in Flushing Meadows, New York City, from August 31 to September 14, 2009. It was the 129th edition of the US Open and the fourth and final Grand Slam tournament of the year.

The tournament comprised events for professional players in singles, doubles and mixed doubles, as well as junior and wheelchair competitions. The main draw singles competition featured 128 players, both men and women. Matches were played on the DecoTurf hard courts.

Juan Martín del Potro won the men's singles title, defeating five-time defending champion Roger Federer in a five-set final. This was del Potro's first Grand Slam title. Kim Clijsters won the women's singles title, defeating Caroline Wozniacki in the final. It was Clijsters' second US Open title and her first Grand Slam title since returning to the sport after a two-year retirement. Bob Bryan and Mike Bryan won the men's doubles title, and Serena Williams and Venus Williams won the women's doubles title. Mark Knowles and Anna-Lena Grönefeld won the mixed doubles title.

The 2009 US Open was notable for several upsets and compelling matches, as well as the resurgence of Kim Clijsters, who entered the tournament as an unseeded wildcard. The tournament was broadcast worldwide.