| Men's doubles | |
|---|---|
| 2021 Serbia Open | |
| Champions |  Ivan Sabanov Matej Sabanov |
| Runners-up |  Ariel Behar  Gonzalo Escobar |
| Final score | 6–3, 7–6(7–5) |
Jonathan Erlich and Andy Ram were the last defending champions after victory in 2012, but Erlich chose not to participate and Ram retired from professional tennis in 2014.
Ivan and Matej Sabanov won the title, defeating Ariel Behar and Gonzalo Escobar in the final, 6–3, 7–6(7–5).
Nikola Mektić / Mate Pavić (Withdrew)
Austin Krajicek / 
Oliver Marach (First round)
Raven Klaasen / 
Ben McLachlan (First round)
Marcelo Arévalo / 
Matwé Middelkoop (First round)| First Round | Quarterfinals | Semifinals | Final | ||||||||||||||||||||||||
| Alt |  A Sitak  S Travaglia | 2 | 6 | [6] | |||||||||||||||||||||||
| A Behar G Escobar | 6 | 3 | [10] | A Behar G Escobar | 6 | 7 | |||||||||||||||||||||
 J Millman J-P Smith | 6 | 6 | J Millman J-P Smith | 4 | 5 | ||||||||||||||||||||||
 M Demoliner  S González | 4 | 3 | A Behar G Escobar | 6 | 6 | ||||||||||||||||||||||
| 4 | M Arévalo M Middelkoop | 4 | 65 |  T Brkić  N Ćaćić | 3 | 4 | |||||||||||||||||||||
| T Brkić N Ćaćić | 6 | 77 | T Brkić N Ćaćić | 0 | 79 | [10] | |||||||||||||||||||||
| WC | M Kecmanović D Lajović | 4 | 4 | S Bolelli  M González | 6 | 67 | [8] | ||||||||||||||||||||
| S Bolelli M González | 6 | 6 | A Behar G Escobar | 3 | 65 | ||||||||||||||||||||||
 R Bopanna P Cuevas | 1 | 0r | WC | I Sabanov M Sabanov | 6 | 77 | |||||||||||||||||||||
 A Bedene D Sharan | 6 | 0 | A Bedene D Sharan | 1 | 3 | ||||||||||||||||||||||
| WC | I Sabanov M Sabanov | 6 | 6 | WC | I Sabanov M Sabanov | 6 | 6 | ||||||||||||||||||||
| 3 | R Klaasen B McLachlan | 4 | 2 | WC | I Sabanov M Sabanov | 711 | 6 | ||||||||||||||||||||
| M Berrettini A Vavassori | 79 | 6 | M Berrettini A Vavassori | 69 | 3 | ||||||||||||||||||||||
A Molteni  F Nielsen | 67 | 4 | M Berrettini A Vavassori | 6 | 77 | ||||||||||||||||||||||
 L Bambridge D Inglot | 65 | 79 | [10] | L Bambridge D Inglot | 4 | 63 | |||||||||||||||||||||
| 2 | A Krajicek O Marach | 77 | 67 | [7] | |||||||||||||||||||||||
Bob Bryan and Mike Bryan were the defending champions and successfully defended their title, defeating Jonathan Erlich and Andy Ram 7–6(8–6), 6–2 in the final.
Bob Bryan and Mike Bryan were the defending champions, but lost in the quarterfinals to Mahesh Bhupathi and Mark Knowles.
Mark Knowles and Daniel Nestor were the defending champions, but lost in the first round to Lukáš Dlouhý and David Škoch.
Jonathan Erlich and Andy Ram defeated Paul Hanley and Kevin Ullyett 7–6(7–4), 7–6(12–10) to secure the title.
Jonathan Erlich and Andy Ram were the defending champions, but Bob Bryan and Mike Bryan defeated them 4–6, 7–6(7–2), [10–7], in the final.
Jonathan Erlich and Andy Ram were the defending champions, but lost in the quarterfinals to Vince Spadea and Fernando Verdasco.
Jonathan Erlich and Andy Ram were the defending champions, but Erlich chose not to participate due to an elbow injury, and only Ram competed that year.
Ram partnered with Max Mirnyi, but lost to Feliciano López and Fernando Verdasco in the second round.
Jonathan Erlich and Andy Ram were the defending champions, but Erlich chose not to participate due to injury, and only Ram competed that year.
Ram partnered with Max Mirnyi, they lost in the final to Mardy Fish and Andy Roddick 6–3, 1–6, [12–14]
Jonathan Erlich and Andy Ram were the defending champions; however, they lost to George Bastl and Chris Guccione in the final. The new champions won 7–5, 7–6(6).
Jonathan Erlich and Andy Ram won in the final 6–3, 7–6(7–4) against Andrew Kratzmann and Jarkko Nieminen.
Jeff Coetzee and Chris Haggard were the defending champions but lost in the first round to Jiří Novák and Petr Pála.
Julian Knowle and Michael Kohlmann were the defending champions but lost in the quarterfinals to Mariusz Fyrstenberg and Marcin Matkowski.
Eric Butorac and Rajeev Ram were the defending champions but decided not to participate.
Christopher Kas and Viktor Troicki won in the final against Jonathan Erlich and Jürgen Melzer 6–4, 6–4.
Mariusz Fyrstenberg and Marcin Matkowski were the defending champions, but were eliminated in the first round by Jonathan Erlich and Andy Ram who won the tournament.
Bob Bryan and Mike Bryan were the defending champions, but lost in the semifinals this year.
Jonathan Erlich and Andy Ram were the defending champions.
Nicolas Mahut and Édouard Roger-Vasselin were the defending champions, but Roger-Vasselin chose not to participate. Mahut played alongside Sergiy Stakhovsky, but lost in the semifinals to Jonathan Erlich and Rajeev Ram.
Chris Guccione and Lleyton Hewitt won the title, defeating Erlich and Ram in the final, 7–5, 6–4.
Julien Benneteau and Nenad Zimonjić were the defending champions, but chose not to participate together. Benneteau played alongside Michaël Llodra, but lost to Jean-Julien Rojer and Horia Tecău in the first round. Zimonjić teamed up with Daniel Nestor, but lost to Juan Sebastián Cabal and David Marrero in the first round.
Łukasz Kubot and Marcelo Melo were the defending champions and successfully defended their title, defeating Alexander and Mischa Zverev in the final, 7–6(7–1), 6–4 in a repeat of the previous year's final.
Bob and Mike Bryan were the defending champions, but Bob Bryan could not participate due to injury. Mike Bryan played alongside Frances Tiafoe, but lost in the quarterfinals to Ryan Harrison and Rajeev Ram.
| Grand Slam events | |
|---|---|
| ATP Tour Masters 1000 | |
| ATP Tour 500 | |
| ATP Tour 250 |
|
| Team events | |
 – Tournaments are affected by the COVID-19 pandemic * – Tournaments are introduced due to the impact of the COVID-19 pandemic | |