The Williams sisters received a wild card for the US Open and will be playing doubles. Since the French Open, the sisters have not played together.
The US Open is believed to be Serena's last tournament as she announced her "evolution" away from tennis in a first-person Vogue essay. Venus hasn't announced any retirement plans yet but has played little over the last year.
The pair won their second Grand Slam doubles together in 1999 at the US Open, having won the French Open earlier in the season, and Serena won her first major title at the same event. Since then they have become two of the most prolific players in the sport's history, and as a team they have won 14 Grand Slam trophies, most recently at Wimbledon in 2016 and three Olympic gold medals.
The draw for the doubles will take place on Wednesday. Serena will play Danka Kovinic on Monday and Venus will play Alison Van Uytvanck on Tuesday in the first round.
There are several pairs that received wild-card entries from the US Open.