Ascending single or double ropes is most often practiced in rope access, tree climbing, caving or technical climbing. Ascending a single rope will often involve a Jumar [1] and a camming device placed on your foot or chest. Ascending a doubled rope can be done with just the rope using Blake's hitch or some extra material and a Prusik knot.

[1]: http://en.wikipedia.org/wiki/Ascender_(climbing)