In doubles, the Rosie Casals Group is Pegula and Gauff, Barbora Krejcikova and Katerina Siniakova, Xu Yifan and Yang Zhaoxuan, and Desire Krawczyk and Demi Schuurs; the Pam Shriver Group is Gabriela Dabrowski and Giuliana Olmos, Veronika Kudermetova and Elise Mertens, Lyudmyla Kichenok and Jelena Ostapenko, and Anna Danilina and Beatriz Haddad Maia.
Pegula and Gauff are the first pair of women entered in both singles and doubles at the WTA Finals since Serena and Venus Williams did it in 2009. No. 3 Pegula and No. 4 Gauff are also the first two American women both ranked in the top four since the Williams sisters in 2010.
Jabeur, Pegula, Gauff and Kasatkina are all appearing at the event for the first time. Since 2000, only twice were there more WTA Finals participants making their singles debuts: In 2001, five women were in the field for the first time, and last year, six were.
The WTA Finals are returning to the United States for the first time since 2005 after the tour moved it out of China for the second year in a row.
The 2021 WTA Finals originally were supposed to be held in Shenzhen, China, but were moved to Guadalajara, Mexico, amid the coronavirus pandemic.