The men's marathon at the 2008 Summer Olympics took place on 24 August at 7:30am in Beijing, ending in the Beijing National Stadium. It was the last time in Summer Olympics history that the start and/or finish of the men's marathon route was located inside the Olympic Stadium. Ninety-five athletes from 56 nations competed. The winner of the event was Samuel Wanjiru of Kenya, who set an Olympic record in the time of two hours, six minutes, and 32 seconds. It was Kenya's first victory in the men's marathon. Morocco won its first medal in the event since 1960, with Jaouad Gharib's silver. Tsegay Kebede of Ethiopia took bronze.

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.