The 2021 Tour de France was the 108th edition of the Tour de France, one of cycling's three grand tours. Originally planned for the Danish capital of Copenhagen, the start of the 2021 Tour (known as the Grand Départ) was transferred to Brest because of the COVID-19 pandemic, with Copenhagen hosting four matches in the UEFA Euro 2020, which had also been rescheduled to 2021 because of the pandemic. Originally scheduled for 2 to 25 July 2021, the Tour was moved to 26 June to 18 July 2021 to avoid the rescheduled 2020 Summer Olympics. This would have been the first occasion on which the Tour de France had visited Denmark. Denmark instead hosted the Grand Départ in 2022.

The race was won for the second consecutive year by Tadej Pogačar of UAE Team Emirates, becoming the youngest rider to win the Tour twice. Pogačar began to build his advantage with his win in the stage 5 time trial. He first took the maillot jaune on stage 8, when he gained almost three and a half minutes on the other contenders after attacking on the penultimate climb of the Col de Romme. He gained another half minute the next day on the summit finish to Tignes. Pogačar rode defensively in the second week before winning both mountaintop finishes at Col de Portet and Luz Ardiden in the third week. He won by 5' 20" over Jonas Vingegaard of Team Jumbo–Visma. Vingegaard was originally supposed to be a domestique for his team's original leader, Primož Roglič. After Roglič's crash and eventual abandon, Vingegaard became the team's leader and rode into form in the second week. He managed to finish second on both mountaintop finishes in the third week before finishing third in the final time trial. Third place went to Richard Carapaz of INEOS Grenadiers, becoming the first Ecuadorian to finish on the podium in the Tour. He emerged as one of the three strongest climbers in the race, along with Pogačar and Vingegaard, before eventually finishing third on both summit finishes in the final week.

In the race's other classifications, Mark Cavendish of Deceuninck–Quick-Step won the points classification for the second time in his career. Cavendish took the green jersey after winning his first Tour stage since 2016 on stage 4. He proceeded to win three more stages to equal Eddy Merckx's record for the most career Tour stage wins. Aside from winning the maillot jaune, Pogačar also won the mountains and young rider classifications for the second successive year. He clinched the win in the mountains classification after his back-to-back wins in the third week, adding 80 points to his tally as both stages' final climbs offered double points. He took the lead in the young rider classification after the first stage and held on to the lead until the end of the race. Team Bahrain Victorious won the team classification while Franck Bonnamour of B&B Hotels p/b KTM won the race's overall combativity award after being involved in several breakaways.

23 teams took part in the 2021 Tour de France. All 19 UCI WorldTeams were entitled and obliged to enter the race, and they were joined by four second-tier UCI ProTeams. Alpecin–Fenix, the best performing UCI ProTeam in 2020, received an automatic invitation, while the other three teams were selected by Amaury Sport Organisation (ASO), the organisers of the Tour. The teams were announced on 4 February 2021. Usually, only twenty-two teams would participate in the race, but for the 2021 season, the Union Cycliste Internationale is allowing the total number of riders to increase from the normal 176 to 184. With team sizes still set at eight riders, the decision allows grand tour organizers to invite one extra wildcard team.

In the lead up to the 2021 Tour de France, Tadej Pogačar (UAE Team Emirates) and Primož Roglič (Team Jumbo–Visma) were seen by many pundits as the top pre-race favourites for the general classification. Their closest rivals were considered to be the trio of Geraint Thomas, Richard Carapaz and Richie Porte from INEOS Grenadiers.

Pogačar was the defending champion and came into the 2021 edition with a successful start to the season, winning the overall classification at Tirreno–Adriatico and the Tour of Slovenia, finishing third at the Tour of the Basque Country, and winning his first Monument at Liège–Bastogne–Liège. After finishing as the Tour runner-up to Pogačar in 2020, Roglič went on to defend his overall title at the 2020 Vuelta a España. In 2021, Roglič finished fifteenth at Paris–Nice before claiming the overall classification at the Tour of the Basque Country. Thomas, the 2018 Tour champion, won the Tour de Romandie before finishing third overall in the lead-up Critérium du Dauphiné which was won by his teammate Porte. Their teammate Carapaz, the 2019 Giro d'Italia champion, won the other lead-up race, the Tour de Suisse.

The other riders considered contenders for the general classification were Rigoberto Urán (EF Education–Nippo), Movistar Team duo Enric Mas and Miguel Ángel López, French riders Julian Alaphilippe (Deceuninck–Quick-Step), Guillaume Martin (Cofidis) and David Gaudu (Groupama–FDJ), 2020 Giro d'Italia champion Tao Geoghegan Hart (INEOS Grenadiers) and fellow podium finisher Wilco Kelderman (Bora–Hansgrohe).

The sprinters considered favourites for the points classification and wins on the flat or hilly bunch sprint finishes were seven-time green jersey winner Peter Sagan (Bora–Hansgrohe), Caleb Ewan (Lotto–Soudal), Arnaud Démare (Groupama–FDJ), Tim Merlier and Mathieu van der Poel (Alpecin–Fenix), Wout van Aert (Team Jumbo–Visma), Sonny Colbrelli (Team Bahrain Victorious), Michael Matthews (Team BikeExchange) and Mark Cavendish, who was a late replacement for the injured defending champion Sam Bennett at Deceuninck–Quick-Step.