The race is split into 21 days of racing, called stages. Each stage is its own mini-race, between roughly 150 and 230 kilometres long. The cyclists race over flat farmland, up huge mountains in the Alps and Pyrenees, and along seaside roads. At the end of each day, all their times are added up.
The rider with the lowest total time wears a special bright yellow shirt called the maillot jaune ('yellow jersey'). Whoever is wearing it at the end of the last day, on the famous Champs-Élysées in Paris, is the winner of the whole Tour.
Cyclists ride in big groups called the peloton (French for 'little ball'). Riding tucked in close behind another cyclist saves a huge amount of energy, because the rider in front pushes the air aside for everyone behind. Teams help their best rider by taking turns at the front.
Millions of people line the roads to watch, often with funny costumes and big flags. Around 12 million people go to see the race live each year, making it one of the most-watched sport events in the world. And unlike most big sports - it is completely free to watch from the side of the road.