[1] The maximum number of athletes per nation had been set at 3 since the 1930 Olympic Congress.

Returning runners from the 1964 marathon included two-time defending champion Abebe Bikila of Ethiopia, fifth-place finisher József Sütő of Hungary, and eighth-place finisher Kenji Kimihara of Japan.

His countryman Mamo Wolde (who had run in 1964 but had not finished, while his brother Demissie Wolde finished 10th) was a "formidable contender," particularly with the high altitude of Mexico City seen as being favorable to the Ethiopian team, used to high altitudes.

[2] Costa Rica, Guyana, Kuwait, Nigeria, the Philippines, Sierra Leone, Uganda, Uruguay, and Zambia each made their first appearance in Olympic marathons; East and West Germany competed separately for the first time.

The United States made its 16th appearance, the only nation to have competed in each Olympic marathon to that point.