The tour, organised by the Paris- based Societe du Tour de France, was launched in 1903 by journalist Henri Desgrange to publicise the sports newspaper, L'Auto.
It is the world's most lucrative cycle race, offering pounds 1.5m in prizes, including pounds 250,000 for the overall winner. There are daily prizes of pounds 6,500 for the stage winners.
The Tour has come to Britain once before, for a stage near Plymouth in 1974. The tour now ventures outside France almost every year, both for commercial reasons and to help promote the event abroad.
There are only two British riders this year, Sean Yates and Chris Boardman. Robert Millar recorded the highest finish for a Briton, fourth in 1984. With his victory in Saturday's time trial Boardman became only the second Briton in history to wear the race leader's yellow jersey. The other to do so was Tommy Simpson, 32 years ago. Although Boardman has little chance of being the overall winner, he could still be wearing the yellow jersey when the race arrives in Britain.
Every rider has a specific role. The leader's goal is overall victory. Some riders specialise in time trials, others are sprinters for the flatter stages and climbers for mountain stages.
The Tour is contested by 21 teams of nine riders. Entry is based on a team's world ranking.
Each team has a large back-up crew, which includes managers, coaches, media handlers, doctors, masseurs, and chefs.
Within the race there are three competitions. The yellow jersey is worn by the rider with the lowest aggregate time; the green by the leader in the points competition, for the most consistent rider in the stages and sprint sections; and the red polka dot by the leader in the King of the Mountains competition.
The Tour lasts for three weeks, with only one rest day. Most stages - one per day - are between 170km and 270km long. The riders will average about 38km an hour (24mph) over the race. About three-quarters of the field can be expected to finish.
This year's tour includes three individual time-trial stages and one team time trial. There are six mountain stages.