The glen is U-shaped, formed by an ice age glacier, about 12.5 km (7.8 mi) long with the floor of the glen being less than 700 m (0.4 miles) wide, narrowing sharply at the Pass of Glen Coe.
The entrance to the glen from the west is below the foot of Buachaille Etive Beag just west of Lochan na Fola, from where waters run east to Loch Leven via the River Coe. The river — Ossian's "dark Cona" — passes over waterfalls at the Pass of Glen Coe before flowing down to the small Loch Achtriochtan. Loch Achtriochtan is Loch Trychardan (loch of the three friends or relatives) in Timothy Pont's map of the area. After the loch the river turns north west, passing through Glencoe village, before flowing into the sea loch of Loch Leven (a salt-water arm of Loch Linnhe) at Invercoe.
The area to east of Lochan na Fola is often classed as part of Glen Coe (see for example the location of Glencoe ski centre), but is in fact part of the upper reaches of Glen Etive.
The south side of the glen is marked by a succession of distinct peaks: Buachaille Etive Beag at the eastern end, followed by the Three Sisters, shoulders of the Bidean nam Bian massif which are subdivided by Coire Gabhail and Coire nan Lochan. The name Coire Gabhail (corrie of the bounty, or hollow of capture) refers to former times when the corrie was used by members of Clan Macdonald to hide cattle and other livestock, whether their own or stolen from others. The wide flat glen is well suited for this purpose since from Glen Coe it appears to be a normal v-shaped glen approached only by a steep narrow gorge. Summits in the Bidean nam Bian massif include Stob Coire Sgreamhach, Stob Coire nan Lochan and Aonach Dubh (the third "sister").
By contrast the north side of the glen is a stark wall of mountain, the Aonach Eagach ridge. The ridge is crossed at the eastern end by the Devil's Staircase, an old military road opposite Buachaille Etive Mòr. The western end terminates with the conical Pap of Glencoe (Sgùrr na Cìche), above Glencoe village, at the point where the glen opens out to Loch Leven.