The 1921 Tour de France was the 15th edition of the Tour de France, taking place 26 June to 24 July. The total distance was 5,485 km (3,408 mi) and the average speed of the riders was 24.720 km/h. The race was won by Belgian Leon Scieur. The Belgians dominated the entire race, partly due to the absence of the French Pélissier brothers, who were on bad terms with the Tour organisation. Scieur's victory was largely uncontested; Hector Heusghem came close after the sixth stage, but lost time later. The organisation tried to get the cyclists to attack more by several means, but this failed.

The 1920 Tour de France had been dominated by Belgian cyclists, who won twelve of the fifteen stages, and the top seven of the overall classification. The French cyclists Henri and Francis Pélissier had left the 1920 Tour de France after Henri received a penalty from the Tour organisation for throwing away a tire, and they were still fighting. Therefore, the Pélissier brothers did not join the 1921 Tour de France. Two veteran cyclists who did join the race were Ernest Paul and Lucien Pothier, both forty years old. Paul rode his first Tour de France in 1908, while Pothier had started in the first Tour de France in 1903, and finished second.

The winner of 1920, Philippe Thys, was the dominant stage racer of the time, but he was recovering from an illness and could not compete for the victory.

The economic impact of World War I was still not over, so as in the previous years there were not sponsored teams, but the cycling companies had bundled their forces under the nick La Sportive. The cyclists were divided in two categories, this time named 1ère class (first class), the professionals, and 2ème classe (second class), the amateurs. This year, some of the second class cyclists would finish higher than some of the first class cyclists.

The 1921 Tour de France saw the introduction of foreign press. They followed the race in their own cars. For the first time, an inhabitant from Monaco joined the Tour de France. Laurent Devalle needed more than twenty-seven hours for the fifth stage, and would finally give up in the eleventh stage.

Overall, the Tour did not have any major events. This troubled the Tour organiser and newspaper owner Henri Desgrange, who sanctioned cyclists that were not combative enough in his view.

In the first stage, Honoré Barthélemy had to fix a flat tire eleven times. Despite this, he still finished in second place behind Louis Mottiat, with Léon Scieur in third place. In the second stage, won by Romain Bellenger, Scieur finished in second place, almost one hour before Mottiat and Barthélemy, so Scieur was leading the race. Scieur improved his lead by winning the third stage, and was already leading by 12'38" over his closest opponent, Hector Heusghem. In the fourth and fifth stage, both won by Mottiat, Scieur managed to increase his lead to almost half an hour.

In the sixth stage, the first real mountains were to be climbed. Hector Heusghem took off on the Tourmalet, reached the top there first, rode solo over the Aspin and the Peyresourde and finished with a 24-minute margin. This brought the difference between Scieur and Heusghem back to slightly over four minutes. The press predicted a new duel between Scieur and Heusghem.