Serena Williams, 40, and Venus Williams, 42, have not played in the same doubles pair since losing in the third round of the French Championships four years ago.
But in the US Open, the last grand slam tournament of the year, it's time again as the sisters have received a wild card to the doubles tournament.
The Williams sisters have enjoyed great success together in doubles.
In total, there have been 14 grand slam titles, including two US Open titles, in 1999 and 2009. In addition, they have won three Olympic gold medals together in doubles.
Serena Williams announced at the beginning of August that "now the countdown has begun".
It is interpreted by many that she will retire after the US Open at home in New York - after more than 20 years at the top of the world.
The US Open starts on Monday.