| Doubles | |
|---|---|
| 2021 Open Castilla y León | |
| Champions |  Robert Galloway Alex Lawson |
| Runners-up | JC Aragone  Nicolás Barrientos |
| Score | 7–6(10–8), 6–4 |
Sander Arends and David Pel were the defending champions [1] but chose not to defend their title.
Robert Galloway and Alex Lawson won the title after defeating JC Aragone and Nicolás Barrientos 7–6(10–8), 6–4 in the final.
Robert Galloway / Alex Lawson (champions)
Arjun Kadhe / 
Gonçalo Oliveira (semifinals) Jeevan Nedunchezhiyan / Purav Raja (first round, retired)
Diego Hidalgo / 
Sergio Martos Gornés (quarterfinals)| First round | Quarterfinals | Semifinals | Final | ||||||||||||||||||||||||
| 1 | R Galloway A Lawson | 6 | 6 | ||||||||||||||||||||||||
 A Cozbinov  P Kotov | 1 | 4 |  F Fallert N Moreno de Alboran | 4 | 4 | ||||||||||||||||||||||
| F Fallert N Moreno de Alboran | 6 | 6 | 1 | R Galloway A Lawson | 6 | 6 | |||||||||||||||||||||
| 4 | D Hidalgo S Martos Gornés | 6 | 6 | WC |  M Vervoort  F Zeballos | 3 | 4 | ||||||||||||||||||||
C Gómez-Herrera  M Jaziri | 4 | 1 | 4 | D Hidalgo S Martos Gornés | 64 | 6 | [9] | ||||||||||||||||||||
N Chappell  R Peniston | WC | M Vervoort F Zeballos | 77 | 4 | [11] | ||||||||||||||||||||||
| WC | M Vervoort F Zeballos | w/o | 1 | R Galloway A Lawson | 710 | 6 | |||||||||||||||||||||
| S Mansouri A Menéndez Maceiras | 2 | 64 | JC Aragone N Barrientos | 68 | 4 | ||||||||||||||||||||||
 M-A Hüsler  R Olivo | 6 | 77 | M-A Hüsler R Olivo | 67 | 62 | ||||||||||||||||||||||
| JC Aragone N Barrientos | 2 | JC Aragone N Barrientos | 79 | 77 | |||||||||||||||||||||||
| 3 | J Nedunchezhiyan P Raja | 1r | JC Aragone N Barrientos | 6 | 6 | ||||||||||||||||||||||
 FC Jianu N Sánchez Izquierdo | 2 | A Kadhe G Oliveira | 3 | 4 | |||||||||||||||||||||||
| John Echeverría A Mendoza | w/o | J Echeverría A Mendoza | 1 | 4 | |||||||||||||||||||||||
| 2 | A Kadhe G Oliveira | 6 | 6 | ||||||||||||||||||||||||
Luke Bambridge and Akira Santillan were the defending champions but chose not to defend their title.
Robert Galloway and Bradley Klahn were the defending champions but chose not to defend their title.
Robert Galloway and Roberto Maytín were the defending champions but only Maytín chose to defend his title, partnering Jackson Withrow. Maytín lost in the final to Diego Hidalgo and Martin Redlicki.
Hans Hach Verdugo and Luke Saville were the defending champions but only Hach Verdugo chose to defend his title, partnering Dennis Novikov. Hach Verdugo lost in the first round to Alex Lawson and Jackson Withrow.
Denys Molchanov and Aleksandr Nedovyesov were the defending champions and successfully defended their title, defeating Robert Galloway and Alex Lawson 6–4, 7–6(7–2) in the final.
Treat Huey and Nathaniel Lammons were the defending champions but only Huey chose to defend his title, partnering Sem Verbeek. Huey lost in the quarterfinals to Emilio Gómez and Roberto Quiroz.
Sadio Doumbia and Fabien Reboul were the defending champions and successfully defended their title, defeating Guido Andreozzi and Guillermo Durán 7–5, 6–3 in the final.
Matías Franco Descotte and Orlando Luz were the defending champions but chose not to defend their title.
Mitchell Krueger and Jack Sock were the defending champions but chose not to defend their title.
Andrés Molteni and Hugo Nys were the defending champions but chose not to defend their title.
Ariel Behar and Andrey Golubev were the defending champions but chose not to defend their title.
Treat Huey and Nathaniel Lammons were the defending champions but chose not to defend their title.
Enzo Couacaud and Albano Olivetti were the defending champions but chose not to defend their title.
Robert Galloway and Alex Lawson were the reigning champions but chose to defend their title with different partners. Galloway partnered Jackson Withrow but lost in the final to William Blumberg and Max Schnur. Lawson partnered Reese Stalder but lost in the semifinals to Galloway and Withrow.
Nuno Borges and Francisco Cabral were the two-time defending champions but only Cabral chose to defend his title, partnering João Domingues. Cabral lost in the quarterfinals to Sadio Doumbia and Fabien Reboul.
Robert Lindstedt and Jonny O'Mara were the defending champions but chose not to defend their title.
William Blumberg and Max Schnur were the defending champions but only Blumberg chose to defend his title, partnering Luke Saville. Blumberg lost in the first round to Juan Pablo Ficovich and Facundo Mena.
Hsieh Cheng-peng and Christopher Rungkat were the defending champions but chose not to defend their title.
William Blumberg and Max Schnur were the defending champions but only Blumberg chose to defend his title, partnering Ben Shelton. Blumberg lost in the semifinals to Constantin Frantzen and Reese Stalder.
Nathaniel Lammons and Jackson Withrow were the defending champions but chose not to defend their title.