The World Cycle Race, being billed as the biggest bike race on the planet, begins today.
With 18,000 miles to ride, the organisers - called The Adventurists - say it is the longest continuous cycle race. There will be five riders on this year's meridian startline in Greenwich, south east London.
Three cyclists, out of the original nine starters, managed to finish the race in 2012 - the only other time it was held.
The five riders must start and finish in the same place, travel in the same direction without crossing back on themselves and pass through two set international locations.
They will make their way on different routes through Europe and on through countries which may include Vietnam, Thailand, India, Australia, New Zealand and the US.
The line-up includes Irish radio presenter Breifne Earley, 32, Indian sock business owner Prasad Erande, 29, along with psychology student Lee Fancourt, 36, and fitness enthusiast Jason Saunders, 24, who are both English.
The fifth cyclist is Fran Hollender, 26 - the only woman - who has been in full-time training for the race. Another 100 cyclists are set to help see them off.
The 2012 winner was Mike Hall who finished in 107 days.
All the competitors are aiming to become the fastest cyclist around the planet. This year the four male riders will be aiming to finish in under 126 days, while Ms Hollender aims to finish in under 151 days.
Dan Wedgwood, of The Adventurists, said: "The riders who are taking part are not professional cycilts - some of them have only been cycling for a year.
"It is about opening up cycling to anyone and anyone can take part in this challenge. It is so much more about the mental cycling ability - anyone can try it if they are prepared to to do a ridiculous amount of training."