This year's Boston Marathon will be the largest ever and here are some facts you may find interesting.
Some 36,000 runners are scheduled to take part. And officials estimate there will be 1 million spectators.
Security will be tight as 3,500 police officers will be on hand to help secure the route.
From start to finish there will be 25,000 feet of ribbon used along the way and race officials are prepared to use 1.4 million paper cups to keep the runners and spectators hydrated.