Trail running is a type of running that takes place on outdoor trails, often in mountainous terrain, and often includes significant ascents and descents. Trail running is overseen by the International Trail Running Association (ITRA) and includes longer races.

Fell running, also sometimes known as 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. It has elements of trail running, cross country and mountain running, but is also distinct from those disciplines.