The 1905 Tour de France was the third edition of the Tour de France, held from 9 to 30 July, organised by the newspaper L'Auto. Following the disqualifications after the 1904 Tour de France, there were changes in the rules, the most important one being the general classification not made by time but by points. The race saw the introduction of mountains in the Tour de France, and René Pottier excelled in the first mountain, although he could not finish the race. Due in part to some of the rule changes, the 1905 Tour de France had less cheating and sabotage than in previous years, though they were not eliminated. It was won by Louis Trousselier, who also won four of the eleven stages.

After the 1904 Tour de France, some cyclists were disqualified, most notably the top four cyclists of the original overall classification, Maurice Garin, Lucien Pothier, César Garin and Hippolyte Aucouturier. Maurice Garin was originally banned for two years and Pothier for life, so they were ineligible to start the 1905 Tour de France. Of these four, only Aucouturier (who had been "warned" and had a "reprimand inflicted" on him), started the 1905 Tour. They were disqualified by the Union Vélocipédique Française, based on accusations of cheating when there were no race officials around. For the 1904 Tour, it was difficult to observe the cyclists continuously, as significant portions of the race were run overnight, and the long stages made it difficult to have officials everywhere.

Because these disqualifications had almost put an end to the Tour de France, the 1905 event had been changed in important ways, to make the race easier to supervise:

The first cyclist to cross the finish line received 1 point. Other cyclists received one point more than the cyclist who passed the line directly before him, plus an additional point for every five minutes between them, with a maximum of ten points. In this way, a cyclist could not get more than 11 points more than the cyclist that crossed the finish line just before him.

As an example for this point system, the result for the first seven cyclists in the first stage is in this table:

The other important introduction were the mountains. One of Desgrange's staffers, Alphonse Steinès, took Desgrange for a trip over the Col Bayard at 1,246 metres (4,088 ft) and the Ballon d'Alsace at 1,178 metres (3,865 ft), that had an average gradient of 5.2% with 10% at some places, to convince Desgrange to use these climbs in the route. Desgrange accepted it, saying that Steinès would take the blame if the mountains would be too hard to climb. In the two previous editions, the highest point was the Col de la République at 1,145 metres (3,757 ft). In 1905, Desgrange chose to overlook this, and focused instead on the introduction of the Ballon d'Alsace, because he saw that he had missed the opportunity for publicity previously.

There were two categories of riders, the coureurs de vitesse and the coureurs sur machines poinçonnées. The riders in the first category were allowed to change bicycles, which could be an advantage in the mountains, where they could use a bicycle with lower gears. The riders in the machines poinçonnées category had to use the same bicycle in the entire race, and to verify this, their bicycles were marked.

Before the race started, 77 riders had signed up for the race. Seventeen of those did not start the race, so the Tour began with 60 riders, including former winner Henri Cornet and future winners René Pottier and Lucien Petit-Breton. The riders were not grouped in teams, but most of them rode with an individual sponsor. Two of the cyclists—Catteau and Lootens—were Belgian, all other cyclists were French. Leading up to the start of the Tour, Wattelier, Trousselier, Pottier and Augereau were all considered the most likely contenders to win the event.