It's the world's most famous bike race and is the biggest annual sporting event: the Tour de France starts on Saturday.
Nearly 200 riders cover over 2,000 miles in just 23 days, mostly in France. But for the first three stages, it's passing through England.
It's well known as one of the toughest, most gruelling sporting challenges, so we wanted to see just how hard it is.
Martin's been to Yorkshire to check out just what the world's top cyclists are up against.