The Tour de France is the world's biggest annual sporting event.
Nearly 200 riders cover over 2,175 miles in just 23 days.
It's fair to say it's a good way to keep fit. If you finish the gruelling tour, you could burn off up to 118,000 calories. That's the equivalent of 26 Mars bars per day.
But do you know your yellow jersey from your polka dot? Your prologue stage from your flat? If not, Newsround is here to help.
What is it?
Basically, it's a huge bike race that takes place every summer. It goes right around France and this year, even pops into Belgium.
Millions of people line the route that's made up of 21 stages raced over 23 days - that means they only have two days off to rest. Ouch.
Twenty-two teams from right across the world are involved in the tour, each has nine riders.
The riders average around 25 miles-per-hour over the entire course but at some points, they'll go a lot faster than that.
|what is the tour de france?|
The race is broken up into 21 different parts or 'stages'. It's not just flat roads, the tour takes the riders up into the mountains too. The stages have different names:
Prologue: Each rider races against the clock in a short (usually under six miles) time trial.
Flat: Despite the name, it doesn't necessarily mean it's perfectly flat. Usually it's big packs of competitors riding together in a big group or 'peloton' for around 125 miles. These end in one of two ways; a 'breakaway' victory by an individual or small group; or typically with a hair-raising bunch sprint.
Individual time trial: Every man against the clock. Similar to a prologue but a little longer. These are shorter stages of around 30 miles (as opposed to 100-125 miles).
Mountain: These come in all shapes and sizes. Climbing from sea level to 2,000 metres sometimes more than once in a day. Tough.
How did it start?
The race was started by Henri Desgrange as a publicity stunt back in 1903.
He came up with the crazy idea of a bike race around France in order to raise the profile of L'Auto, the newspaper he worked for.
The first race was a huge success with 60 riders covered an amazing 1,500 miles.
What are the jerseys all about?
The Green Jersey is given to the best sprinter. Britain's Mark Cavendish is one of the world's best in this category, reaching speeds over 40 miles-per-hour.
But the tour isn't just about reaching the highest speeds - it's also known for its up-hill struggles. The riders climb thousands of metres up Alpine mountains, with the best rider on those stages winning a snazzy red and white Polka Dot Jersey.
The White Jersey is given to the best young rider - that's someone who's under 25 years old.
But the prize everyone wants is the Yellow Jersey. If you are in it, you are the overall race leader on total time since the start of the Tour.
Tour champions are often good at climbing, sprinting and time trialling.
Is it all about individuals?
No. It's a big team event but the team leader is very important. He's usually the stronger rider.
The other team members are traditionally called domestiques, from the French word for servants.
These riders work hard in every stage to protect their team leader.
If he gets a puncture, they will wait while the team mechanic changes his wheel.
The star-man will ride behind his team mates to get into their slipstream- that means there's less air resistance for him and it's easier to go fast.
Their reward is a share of the prize money and the glory of contributing to a successful team.
It's called the Tour de France but has it ever left the country?
It regularly nips into other countries that border France.
The first two days of racing, the Grand Depart, are held in a new location every two years. It was in London in 2007 and even the county of Yorkshire has bid to hold the start of the event in 2016!
Click for lessThe 2013 Tour de France will be the 100th Tour de France. It is scheduled to start in Corsica, in the city of Porto-Vecchio. The island will host the first three stages.Corsica is currently the only Metropolitan department through which the Tour has never passed and the organisers wanted to combine the 100th edition of the Tour with the Tour's first ever visit to Corsica.