Mo Farah's attempt to win the London Marathon on his debut and David Weir's bid for his seventh title are among the highlights of the 2014 race on Sunday.
Double Olympic gold-medal winner Farah, 31, faces a strong field and has made the British record his first target.
Weir is aiming to overtake Baroness Tanni Grey-Thompson's haul of six wins in the wheelchair race, a record she has shared with Weir since 2012.
The 30,000-strong race will also feature thousands of amateur runners.
Farah will face the biggest test of his career, knowing his two Olympic titles and three World Championship crowns on the track will count for nothing.
Lining up against the home favourite will be world-record holder Wilson Kipsang, reigning champion Tsegaye Kebede, course record holder Emmanuel Mutai and Olympic and world champion Stephen Kiprotich.
Geoffrey Mutai, who has run the fastest ever marathon - albeit on a Boston course ineligible for record purposes - will be there, too. He is one of seven athletes in the field who have run under two hours five minutes.
The race will feature four of the fastest 10 marathon runners in history. Even the pacemaker is a great, with double Olympic gold medalist Haile Gebrselassie instructed to set up a world record attempt. Kipsang's current mark, set in Berlin last September, stands at 2hrs 3mins 23secs.
It all adds up to an almighty task for Farah, unproven over 26.2 miles. How his body will cope with the step up in distance is the great unknown, especially after he collapsed at the end of the New York half marathon in March, and there are question marks over how his loping running style will translate to the marathon.
One thing is guaranteed: his preparations, under the guidance of coach Alberto Salazar, will have been meticulous.
Salazar said: "There have been a lot of people that are great at shorter events and aren't as good in the marathon. And what's the reason for that?
"One, physically there's something there; their energy systems are more suited for shorter races. Number two is the psychological part.
"The psychological part, forget. Mo is just so tough there's no way the psychological part is going to be a problem. So it could only be some physiological thing, but I doubt it."
The other Britons in the elite race are Scott Overall, Craig Hopkins and debutants Chris Thompson and Ben Livesey.
Weir, who raced to four gold medals at the London Paralympics two years ago, was on antibiotics as he struggled with a chest infection last week.
But the 34-year-old was able to train through the illness and insists he is in "very good shape" as he attempts to record a seventh London victory.
"I seems like I'm stuck on six at the moment - six Paralympic golds, six World Championship golds and six London Marathons - so it is getting to me a bit and I really want to put every effort in on Sunday," Weir said.
In the women's race, another track great will run her first marathon as Ethiopia's Tirunesh Dibaba, the reigning Olympic and world 10,000m champion, makes the step up.
Dibaba has three Olympic and five World Championship titles over 5,000m and 10,000m to her name, but, like Farah, will have a tough field to contend with.
Priscah Jeptoo of Kenya will seek to defend her title, while Ethiopia's London 2012 champion Tiki Gelana, will hope for better luck than she experienced 12 months ago when her hopes were ended by a collision with a wheelchair racer. The British challenge will come from Amy Whitehead and Emma Stepto.