The Polytechnic Marathon, often called the Poly, was a marathon held annually between 1909 and 1996, over various courses in or near London. It was the first marathon to be run regularly over the distance of 26 miles, 385 yards which is now the global standard. A total of eight world marathon bests were set in the Poly, including the first authenticated time under 2 hours, 20 minutes which had been regarded as the marathon equivalent of the four-minute mile. At the time of its demise in 1996, the Poly was Europe's oldest regular marathon. It had seen more world records and had been run over 42.195 kilometres (26.219 mi) more often than any other marathon.

The marathon is a long-distance foot race with a distance of 42.195 km, usually run as a road race, but the distance can be covered on trail routes. The marathon can be completed by running or with a run/walk strategy. There are also wheelchair divisions. More than 800 marathons are held throughout the world each year, with the vast majority of competitors being recreational athletes, as larger marathons can have tens of thousands of participants.