Coordinates: 54°34′35″N 2°55′51″W / 54.576303°N 2.930905°W / 54.576303; -2.930905

Aira Force is a waterfall in the English Lake District, in the county of Cumbria. The word force, from Old Norse fors, is used in many parts of northern England as a synonym for "waterfall".

The stream which flows over the waterfall is Aira Beck, which rises on the upper slopes of Stybarrow Dodd at a height of 720 metres (2,362 ft) and flows north-easterly before turning south, blocked by the high heather-covered slopes of Gowbarrow Fell. It turns south on its eight-kilometre journey to join Ullswater, at a height of 150 metres (492 ft). One kilometre before entering the lake, the beck makes the 20 metres (66 ft) leap down a rocky ravine at the falls known as Aira Force.

Aira Force lies on land owned by the National Trust. The Trust has provided facilities, such as car parking, disabled access, graded paths, and viewing platforms to make Aira Force one of the most famous and most visited waterfalls in the Lake District. A small arched bridge spans the stream just as the beck goes over the falls giving a spectacular view from the top as the water makes its magnificent leap.