On 15 April, the second of the six World Marathon Majors, takes place on the streets of Boston, Massachusetts.
For the 2019 edition, around 30,000 runners are expected to take on the famous 26.2-mile (42.2 km) course.
Last year, heavy rain and strong winds made it a real test with the elite races throwing up some big surprises.
Conditions are still expected to be wet, but less gruelling 12-months on.
We have all the information you need to enjoy the Olympic Channel live stream (if you live in Australia, India or Mexico) - from start times to the course layout, plus all the best storylines ahead of the big day.
Rain ends U.S. drought
It was a torrent that ended a 33-year drought, with no American woman winning the race since Lisa Larsen Weidenbach in 1985.
Desiree Linden had few expectations and even told compatriot Shalane Flanagan, winner of the 2017 New York Marathon, less than a quarter of the way through the race that this would not be her day.
Linden even slowed down while Flanagan stopped for a toilet break.
But as the leaders suffered, 2011 runner-up Linden bridged the gap before pulling clear four miles from home to complete an improbable victory.
She told Runner’s World, "It didn't come out in tears. It was just disbelief. We were hugging and screaming, 'I can't believe that just happened'".
Linden led home an American one-two, but the identity of the runner-up was an even bigger shock.
The internet collectively asked, ‘Who is Sarah Sellers?’ when the nurse without a pro contract finished ahead of more illustrious competitors.
“When you put your head down when the conditions are tough – really crazy things can happen,” she said to the Olympic Channel Podcast.
Sellers, Linden, and the rest of the elite women, will set off at 9.32am (Eastern Daylight Time) in the 2019 edition.
Sarah Sellers – the nurse who finished second at the 2018 Boston Marathon
Sarah Sellers – the nurse who finished second at the 2018 Boston MarathonThe American took on the favourites and won to make her dream a reality. But the success came with an unexpected pressure.
Podcast: The nurse who took a surprise second place at the Boston Marathon
Podcast: The nurse who took a surprise second place at the Boston MarathonSarah Sellers beat the odds to finish second in the 2018 Boston Marathon. The Olympic Channel Podcast spoke to the full-time nurse about what’s changed a year on, her Tokyo 2020 chances, and why she will never pay for a first class flight.
The Japanese 'citizen runner' turned pro
Yuki Kawauchi sprung a huge surprise to take victory in the men's race in 2018.
The Japanese amateur went out hard, with TV race commentators calling it "a crazy move" and claiming he was merely "thinking of getting on camera".
They were clearly unfamiliar with the 'Citizen Runner' who has more sub-2:20 marathon finishes than anyone else on record, and came ninth at the 2017 World Championships.
For years, Kawauchi had been juggling his full-time job as a high school administrator with a running schedule which had included at least 10 marathons, 10 half-marathons - occasionally in a suit or a panda outfit - and the odd ultra-marathon per year.
And the inclement weather of Boston in 2018 presented an opportunity which the then-31-year-old grabbed with both hands.
"I thought this would be my last chance to change my career considering my age," he told Olympic Channel.
While other runners toiled in the conditions, Kawauchi pressed on remorselessly to win in 2:15.58, more than two minutes clear of defending champion Geoffrey Kirui.
Twelve months on, Kawauchi's thoughts turned reality. He became a professional runner on 1st April 2019, with the aim of winning a berth for the host nation at Tokyo 2020.
And he's determined to put up a spirited defence of his title even if the rain stays away this time.
"Among the runners [at Boston 2019], my current personal best is the 16th best. So it will be really challenging to win again."
"My goal is to be in the top three, and at least in the top 10.” - Kawauchi to Olympic Channel
A new player for Team USA
There’s been an interesting addition to the home team, in the form of London 2012 10,000m Olympic silver medallist Sally Kipyego.
Representing the Texas Tech Red Raiders a decade ago, the Kenyan-born runner became one of the most successful female athletes in US Collegiate history.
After giving birth in June 2017, Kipyego decided to represent her adopted country of the United States in the hope of making the Tokyo 2020 marathon team.
And she told Olympic Channel that the arrival of daughter Emma has helped spur her ambitions.
"That's another motivation. I’m so happy that I get to run when she’s here because then she gets to see her mum running.
"She also gets to see me work hard and get to see me enjoy what I do.
"My target is to have a decent race considering how long I have been out.
"I want to have a solid performance. If that means being on the podium, that's fantastic. If it means being number five, that's great. If it means being number 10, that's OK. My target is to just finish strong."
The 33-year-old will be running only her third full marathon after a difficult debut at the New York race in 2015.
She dropped out, but returned the following year and finished second.
The 2011 World 10,000m silver medallist postponed her comeback last year after contracting malaria and pneumonia.
"I ran my first marathon while pregnant, so I had to miss the whole of 2017 and delayed my comeback last year. So a lot of things that happened, family changes, getting my American citizenship, I was getting sick a lot. It was a disappointing time for me.
"But at the same time I always look at the bigger picture. I want to run several years down the road. I'm now confident and healthy. I am not be on the best shape of my life but I am on my way back, am in a good place, decent shape."
Don’t be fooled by her age.
Even at 40, the 2017 Boston Marathon champion, Edna Kiplagat, has ruled out quitting competitive running at any time soon.
"I will go as far as my body is still responding well. I have not even thought of retiring at this point," she said to Olympic Channel.
"If I compare where I was in terms of training in 2017 - now I am at the same level.
"Obviously, Desi Linden is a woman to watch. But as usual I always like running and focusing on my own race."
And should Boston go to plan, Kiplagat is aiming to compete at the IAAF World Championships in Qatar at the end of September.
"I should be in a strong position to challenge for the title in Doha.
"This year will define how my season and next year will be, because I would love to run at the Olympics in Tokyo next year."
The double World marathon champion has her mind on matching the success of Kenyan compatriot Catherine Ndereba.
Ndereba, now retired, is the only other woman to have won two gold medals at the Worlds, and is a four-time winner of the Boston marathon.
"I have had smooth and hard training which is good for me.
"If I compare where I was in terms of training in 2017 and now, I'm at the same level. I am hoping for a perfect run this year, and regain my title."
Kirui ready for action
Geoffrey Kirui is also hoping that he can build a foundation in the United States before the World Championships.
The Kenyan won Boston and the world title in 2017 before finishing runner-up to Kawauchi last year.
"I can’t really compare my current form with 2017," he told Olympic Channel.
"But one thing I know is that I am in tip-top shape."
The self-coached 26-year-old, barely three years into full marathon running, is proving to be the new top talent to watch in 2019 and beyond.
He's banking on his knowledge of the course to regain the title, weather permitting.
"Looking at the elite line-up, it is an exciting field. But you know if you come with your fast time, that rarely counts for a tricky, hilly course like Boston. It is very unpredictable.
"I have now run twice, so I have an idea where the hills are to attack, and when I run I visualize the course. It’s the kind of marathon, where you need to approach tactically, and with some technique, and aim for a strong finish."
Hug looking to maintain dominance in wheelchair race
Switzerland's four-time defending champion Marcel Hug is favourite to retain the title on the Eastern Seaboard, especially after Six-time Paralympian David Weir pulled out of the men's wheelchair race with a foot infection.
Like Hug, Tatyana McFadden is back to defend her title in Boston as she continues her preparations for Tokyo 2020.
The winner of 17 Paralympic medals at four Games, including seven golds, is the hottest favourite of all after five wins in the last six renewals.
McFadden was fourth in 2017 behind Switzerland's Manuela Schaer, as she recovered from life-threatening blood clots in her legs.
But she was back to her best in the rain last year, finishing more than 15 minutes clear of the field.
The Boston Marathon is the world's oldest annual marathon, first held in 1897 having been inspired by the 1896 Olympic Games.
It takes place on the third Monday of April, a state holiday in Massachusetts and Maine called Patriots' Day which marks the start of the American War of Independence.
The iconic race starts in Hopkinton and ends on Boylston Street, but the layout means no time can be classified as a world record.
One of the most notable points on the course is 'Heartbreak Hill' – a steep incline around the 20-mile mark.
Sadly, the race will long be remembered for the tragedy which marred the 2013 event.
Two homemade bombs were set off at the finish line, killing three people and injuring hundreds.
The perpetrators, a pair of Islamist extremists, then shot dead a policeman as they sought to escape the subsequent manhunt.
Each year, the four deaths are remembered at the site of the first explosion.
And a permanent memorial to the fallen, designed by Bolivian-born artist Pablo Eduardo, will be completed around the middle of 2019.
Where to watch
For those living in India, Australia, and Mexico - Olympic Channel is the only place to watch the live stream.
Full details on where to watch in other countries is on the official website which has a full list.
Start times (all in Eastern Standard Time)
9:02am: Wheelchairs and other adaptive racers
9:32am: Elite women
10:00am: Elite men
10:02am: Amateur runners start