Thousands of fun runners and amateur athletes will line up alongside a host of celebrities and elite sportsmen and women at the 32nd London Marathon.
Organisers said just over 37,500 entrants had registered for the event, which begins in Greenwich, south-east London at 9am.
Forecasters predicted dry and bright weather as the race gets under way, but warned there was a chance of rain later on. It should also be the perfect temperature for participants, with highs of around 13C expected.
The London Marathon always attracts a number of famous faces on the start line, and shadow chancellor Ed Balls has said he is just hoping to get round the course. The Morley and Outwood MP is running the marathon for the charities Action for Stammering Children and Whizz Kids, which provides equipment to help disabled youngsters live full lives.
BBC newsreader Sophie Raworth, chef Gordon Ramsay, and model Nell McAndrew are among the celebrities hitting the streets to raise money for charity.
Raworth said she hopes to "stay upright" after collapsing during last year's event. She crashed into a barrier on the side of the road and blacked out after 23 miles. McAndrew is trying to break the three-hour mark for the first time at her sixth London Marathon. Her past times have been so quick that she has qualified to compete with the elite athletes.
A soldier who was blinded by an explosion in Afghanistan will run alongside an actor from Downton Abbey. Lance Bombardier Rob Long said he would require "extreme concentration" to complete the course. He is part of a three-man team that includes Lachlan Nieboer who played a blinded soldier in the latest series of the hit ITV drama.
"Extreme concentration is the main thing," said the 24-year-old, who is running for Blind Veterans UK. "I can only see exactly what is underneath my feet. It takes a lot of concentration to keep the rhythm and pace going. I've built up a lot of trust with my running partner."
Meanwhile over 100 runners will try to break a series of bizarre marathon-related world records. Sasha Kenney, 34, hopes to raise over £2,000 for the NSPCC as she bids to break the six-hour mark for quickest runner hula hooping.
George and Charley Phillips, from Hammersmith, west London, will attempt to beat a time of 8 hours and 25 minutes to become the fastest marathon runners on stilts. And the record for the tallest costume to complete a marathon could be broken by David Lawrenson, 39, from Lancashire, who is donning a 24ft version of the Blackpool Tower.