Cross country running is a sport in which teams of runners race on open-air courses over natural terrain. The course, typically 4–12 kilometres (2.5–7.5 mi) long, may include surfaces of grass and earth, pass through woodlands and open country, and include hills and flat ground. It is both an individual and a team sport, as runners are judged on an individual basis and a points scoring method for teams. Both men and women of all ages compete in cross country, which usually takes place during autumn and winter, and can include weather conditions of rain, sleet, snow or hail, and a wide range of temperatures.

Cross country running is one of the disciplines under the umbrella sport of athletics, and cross country athletes often compete in long-distance track and road events. Although open-air running competitions are pre-historic, the rules and traditions of cross country racing emerged in Britain. The English championship became the first national competition in 1876 and the International Cross Country Championships was held for the first time in 1903. Since 1973 the foremost elite competition has been the IAAF World Cross Country Championships.

One variation on traditional cross country is mountain running, which incorporates significant uphill and/or downhill sections as an additional challenge to the course. Orienteering is another competitive sport similar to cross country, although it features an element of navigation absent from the set and marked courses of cross country.