Beinn Eighe (Scottish Gaelic for 'file mountain') is a mountain massif in the Torridon area of Wester Ross in the Northwest Highlands of Scotland. Lying south of Loch Maree, it forms a long ridge with many spurs and summits, two of which are classified as Munros: Ruadh-stac Mòr at 1,010 m (3,314 ft) and Spidean Coire nan Clach at 993 m (3,258 ft). Unlike most other hills in the area it has a cap of Cambrian basal quartzite which gives the peaks of Beinn Eighe a distinctive light colour. Its complex topography has made it popular with both hillwalkers and climbers and the national nature reserve on its northern side makes it an accessible mountain for all visitors.

Located between Loch Maree and Glen Torridon on the west coast of Scotland, Beinn Eighe is a complex mountain. The main ridge runs on a line extending from close to the village of Kinlochewe in the north-east to the narrow glen of the Coire Dubh Mòr, which separates it from the neighbouring mountain of Liathach to the south-west. The slopes into Glen Torridon on the south side are steep with few features and are covered in white quartzite screes. On the north side are four large corries between which are spurs extending out from the main ridge. The southern and eastern sides of the mountain are flanked by the A896 and A832 roads, however the area to the northwest is largely unpopulated, comprising the mountainous landscape of the Torridon Hills and the Flowerdale Forest.

The eastern half of Beinn Eighe is owned by NatureScot, who manage it as a national nature reserve, whilst the rest of the southern side is owned by the National Trust for Scotland: this area is also managed as part of the reserve. The remaining northwestern part of Beinn Eighe lies within the Grudie & Talladale Estate.

Two of Beinn Eighe's summits are classified as Munros. The highest point Beinn Eighe, Ruadh-stac Mòr ('Big Red Stack' in Scottish Gaelic), lies on one of the spurs off the main ridge and stands at a height of 1,010 m (3,314 ft). Spidean Coire nan Clach ('Peak of the Corrie of Stones' in Scottish Gaelic), which was added to the list of Munros in 1997 to become the second Munro on Beinn Eighe, is the highest point on the main ridge itself. It stands at a height of 993 m (3,258 ft) and commands an extensive view over both Glen Torridon and the rest of the Beinn Eighe massif. Ruadh-stac Beag (896 m (2,940 ft)), which lies on a spur from the main ridge east of Ruadh-stac Mòr, has sufficient relative height to be classified as a Corbett.

One of the most famous features of Beinn Eighe is the corrie of Coire Mhic Fhearchair, often simply known as the "Triple Buttress Corrie" after the three large rock features which dominate the view from the north. There are many rock climbs on the buttresses and hillwalkers can access the tops of the buttresses from the head of the corrie.

In common with much of the Northwest Highlands, the underlying rocks of the area are composed of Lewisian gneiss, a very ancient rock type. The younger Precambrian Torridonian Sandstone, which sits on top of the gneiss, forms the bulk of all of the Torridon Hills, including Beinn Eighe, and was formed around 800 million years ago from the sediment of rivers that flowed across the landscape of the gneiss. Beinn Eighe is however unusual amongst the Torridon Hills in that the summit ridge is composed of white-coloured Cambrian basal quartzite. This is a very hard but brittle rock, that was laid down around 540 million years ago as pure white sands during a period when the area was flooded by warm tropical seas. The quartzite gives Beinn Eighe its familiar light coloured summits, which form a notable contrast to the other peaks in the area, and can appear similar to a covering of snow on the mountain. Within the Cambrian rocks a distinct rock layer, known as the Fucoid Beds, has been identified. The fossils found in the Fucoid Beds are very different to those from rocks of a similar age found in England, a fact that was crucial in establishing that during the Cambrian period the two land masses were separated by ocean. These fossils, which include trilobites, and worm burrows, are some of the oldest fossils to be found in Scotland. The fossil of one creature identified in the rocks of Beinn Eighe, Olenellus armatus, has not been found at any other location.

The area was heavily sculpted by glaciers during successive ice ages.

Many rare plants, including two variants of dwarf shrub heath and a western variant of moss heath, are to be found at Beinn Eighe. In total 680 different species of plants have been identified, including the greatest variety of oceanic mosses and liverworts of any single site in Britain. The summit plateau is the only location in Britain at which the liverwort Herbertus borealis (northern prongwort) has been found; whilst Beinn Eighe is also the most northerly known global location at which the moss species Daltonia splachnoides has been identified. Other rare plant species found include tufted saxifrage and brook saxifrage.