Fell running, also known as mountain running and hill running, is the sport of running and racing, off road, over upland country where the gradient climbed is a significant component of the difficulty. The name arises from the origins of the English sport on the fells of northern Britain, especially those in the Lake District.

Fell races are organized on the premise that contenders possess mountain navigation skills and carry adequate survival equipment as prescribed by the organizer.

The first recorded hill race took place in Scotland. King Malcolm Canmore organised a race in Braemar in 1040 or perhaps as late as 1064, reputedly to find a swift messenger. This event appears to have been a precursor to the Braemar Gathering. There is no documented connection between this event and the fell races of the 19th century. By the 19th century records begin to appear of fell races taking place as a part of community fairs and games. The sport was a simple affair and was based upon the community's values for physical ability. Fell races took place alongside other sports such as wrestling, sprint races and, especially in Scotland, heavy events such as throwing the hammer. These fairs or games events were often commercial as well as cultural, with livestock shows and sales taking place alongside music, dancing and sports. In a community of shepherds and agricultural labourers comparisons of speed and strength were interesting to spectators as a source of professional pride for competitors. A fast shepherd or a strong labourer were as respected, one imagines, as any top ranking colleague in a more modern employment. The most famous of these events in England is the Grasmere Sports meeting in the Lake District, with its Guide's Race. This event still takes place every year in August.