The 2021 Stockholm Open was a professional men's tennis tournament played on indoor hard courts. It was the 52nd edition of the tournament, and part of the ATP Tour 250 series of the 2021 ATP Tour. It took place at the Kungliga tennishallen in Stockholm, Sweden from 7 to 13 November 2021. Unseeded Tommy Paul won the singles title.[1]
See main article: 2021 Stockholm Open – Singles.
Tommy Paul defeated 
Denis Shapovalov, 6–4, 2–6, 6–4Paul won his first ATP Tour title.[2]
See main article: 2021 Stockholm Open – Doubles.
Santiago González / 
Andrés Molteni defeated 
Aisam-ul-Haq Qureshi / Jean-Julien Rojer 6–2, 6–2.| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
| Jannik Sinner | 9 | 1 | ||
| Félix Auger-Aliassime | 11 | 2 | ||
| Denis Shapovalov | 19 | 3 | ||
| Dan Evans | 24 | 4 | ||
| Taylor Fritz | 26 | 5 | ||
| Alexander Bublik | 36 | 6 | ||
| Márton Fucsovics | 40 | 7 | ||
| Frances Tiafoe | 41 | 8 |
The following players received wildcards into the singles main draw:
The following players received entry from the qualifying draw:
The following players received entry as lucky losers:
Nikoloz Basilashvili → replaced by Tommy Paul
Alex de Minaur → replaced by 
Adrian Mannarino Arthur Rinderknech Taylor Fritz Ugo Humbert → replaced by 
Alejandro Davidovich Fokina
Hubert Hurkacz → replaced by 
Egor Gerasimov
Aslan Karatsev → replaced by Nino Serdarušić Gaël Monfils → replaced by 
Márton Fucsovics
Cameron Norrie → replaced by Peter Gojowczyk
Casper Ruud → replaced by Mackenzie McDonald Diego Schwartzman → replaced by Frances Tiafoe
Lorenzo Sonego → replaced by 
Jozef Kovalík
Emil Ruusuvuori| Country | Player | Country | Player | Rank1 | Seed | |
|---|---|---|---|---|---|---|
| Ivan Dodig |  Brazil | Marcelo Melo | 35 | 1 | ||
 New Zealand | ||||||
| United Kingdom | Ken Skupski | United Kingdom | Neal Skupski | 76 | 3 | |
 Kazakhstan | Alexander Bublik | Kazakhstan | Andrey Golubev | 79 | 4 |
The following pairs received wildcards into the doubles main draw:
The following pairs received entry into the doubles main draw as alternates:
Santiago González → replaced by Santiago González / Andrés Molteni Simone Bolelli / Máximo González → replaced by 
Tomislav Brkić / 
Nikola Ćaćić 
Rohan Bopanna / Denis Shapovalov → replaced by Ariel Behar / 
Gonzalo Escobar 
Sander Gillé / Joran Vliegen → replaced by Emil Ruusuvuori / Botic van de Zandschulp Aisam-ul-Haq Qureshi / Jean-Julien Rojer Raven Klaasen / 
Ben McLachlan → replaced by Fabrice Martin / Hugo Nys
Horia Tecău → replaced by Pedro Martínez / Andrea Vavassori Jamie Murray / Bruno Soares → replaced by Taylor Fritz / Tommy Paul John Peers / Filip Polášek → replaced by 
Karl Friberg / 
Mohamed Safwat Michael Venus → replaced by Simon Freund / Nino Serdarušić