Helvellyn (; possible meaning: pale yellow moorland) is a mountain in the English Lake District, the highest point of the Helvellyn range, a north–south line of mountains to the north of Ambleside, between the lakes of Thirlmere and Ullswater.

Helvellyn is the third-highest point both in England and in the Lake District, and access to Helvellyn is easier than to the two higher peaks of Scafell Pike and Scafell. The scenery includes three deep glacial coves and two sharp-topped ridges on the eastern side (Striding Edge and Swirral Edge). Helvellyn was one of the earliest fells to prove popular with walkers and explorers; beginning especially in the later 18th century. Among the early visitors to Helvellyn were the poets Samuel Taylor Coleridge and William Wordsworth, both of whom lived nearby at one period. Many routes up the mountain are possible so that it may be approached from all directions.

However, traversing the mountain is not without dangers; over the last two hundred years there have been a number of fatalities. The artist Charles Gough is more famous for his death on Striding Edge in 1805 than for what he achieved in his life. Among many human feats upon the mountain, one of the strangest was the landing and take-off of a small aeroplane on the summit in 1926. Since early 2018 the summit of Helvellyn including both Striding and Swirral Edges and the wider Glenridding Common are now managed by the John Muir Trust, a wild places conservation charity under a three-year lease with the Lake District Park Authority.