Stephens, a former world number 11, won her first WTA title at the tournament in 2015 and will be looking to continue her comeback from injury, whilst world number two Halep will be making her tournament debut as she looks to continue her recent good form which has seen her come close to the world number one ranking.
The tournament begins in less than two weeks, with Stephens and Halep joining the likes of Kristina Mladenovic and Anastasia Pavlyuchenkova in a highly competitive field.
Stephens looks to continue comeback whilst Halep continues number one quest
There is no doubt that the two head to Washington with different aims, with Halep aiming to continue her quest for world number one and Stephens looking to continue her comeback from a foot injury.
Halep has twice lost when she could have risen to the top spot, in the French Open final and the Wimbledon quarterfinals, though will be in contention for the top spot over the summer. The Romanian has had a fairly strong season, highlighted by a title in Madrid, and will almost certainly be the favorite for the title in Washington when action begins.
Meanwhile, Stephens will be looking for ranking points after missing almost a year of action due to injury. The American, who won three WTA titles in the early stages of last season, returned to the tour at Wimbledon, and will be looking for a good result at a tournament where she won the title in 2015; unseeded two years ago, Stephens beat Samantha Stosur in the last eight before easing past Anastasia Pavlyuchenkova in the final to win her first WTA title.