Varatchaya Wongteanchai and Yang Zhaoxuan were the defending champions, but chose not to participate together. Wongteanchai played alongside Nao Hibino, but lost in the quarterfinals to Ashleigh Barty and Casey Dellacqua. Yang teamed up with Shuko Aoyama, but lost in the quarterfinals to Elise Mertens and İpek Soylu.
Raluca Olaru and Olga Savchuk were the defending champions, but lost in the quarterfinals to Veronika Kudermetova and Aryna Sabalenka.
Kiki Bertens and Johanna Larsson were the defending champions, but Bertens chose not to participate this year. Larsson played alongside Eugenie Bouchard, but lost in the first round to Rika Fujiwara and Darija Jurak.
Victoria Rodríguez and Bibiane Schoofs were the defending champions, but Rodríguez chose not to participate this year.
Naomi Osaka was the defending champion, but lost to Belinda Bencic in the fourth round.
This was the first edition of the tournament.
Ashleigh Barty won her first Miami Open title, beating Karolína Plíšková 7–6(7–1), 6–3 in the singles tennis final. As a result of this victory, she entered the top 10 in the WTA Rankings for the first time. Sloane Stephens was the defending champion, but lost in the third round to Tatjana Maria.
Naomi Broady and Sara Sorribes Tormo were the defending champions, but Broady chose not to participate and Sorribes Tormo chose to compete in Charleston instead.
Kirsten Flipkens and Elise Mertens were the defending champions, but chose not to participate.
Desirae Krawczyk and Giuliana Olmos were the defending champions, but Krawczyk chose not to participate. Olmos partnered alongside Alexa Guarachi but lost in the first round to Harriet Dart and Heather Watson.
Elise Mertens and Demi Schuurs were the defending champions, but chose not to participate together. Schuurs teamed up with Anna-Lena Grönefeld, but lost in the semifinals to Mertens and Aryna Sabalenka.
Shuko Aoyama and Yang Zhaoxuan were the defending champions, but chose not to participate.
Jil Teichmann was the defending champion, but chose to participate in Lexington instead.
Tímea Babos and Kristina Mladenovic were the defending champions and successfully defended their title, defeating Alexa Guarachi and Desirae Krawczyk in the final, 6–4, 7–5.
Tímea Babos and Kristina Mladenovic were the defending champions, but did not defend their title after Mladenovic withdrew because of injuries.
Hsieh Su-wei and Barbora Strýcová were the two-time defending champions, but they chose not to participate.
Shuko Aoyama and Ena Shibahara won the title, defeating Hayley Carter and Luisa Stefani in the final, 6–2, 7–5.
The 2021 İstanbul Cup is a tennis tournament played on outdoor clay courts. It is the 14th edition of the İstanbul Cup, and part of the WTA International tournaments of the 2021 WTA Tour. It will take place in Istanbul, Turkey, from 19 through 25 April 2021.
Anna-Lena Grönefeld and Alicja Rosolska were the defending champions, having won the title of the last edition 2019, however Grönefeld retired in 2019, whilst Rosolska chose not to participate.
Patricia Maria Țig was the defending champion, but she chose not to participate this year.
Veronika Kudermetova 
Elise Mertens 
Nao Hibino 
