Cairn O' Mounth/Cairn O' Mount (Scottish Gaelic: Càrn Mhon) is a high mountain pass in Aberdeenshire, Scotland. The place name is a survival of the ancient name for what are now the Grampian Mountains, earlier called "the Mounth" (in Gaelic: "monadh", meaning mountains). The name change happened from circa 1520 AD. The Ordnance Survey shows the name as Cairn o' Mount.
It has served as an ancient military route at least from Roman times through the 13th century AD. The alignment of the Cairnamounth, Elsick Mounth and Causey Mounth ancient trackways had a strong influence on the medieval siting of many fortifications and other settlements in the area comprised by present-day Aberdeenshire on both sides of the River Dee.
Cairn O' Mounth is at 1493 feet (454 m) above mean sea level, and there are various commanding views of the surrounding landscape which extend as far as the North Sea.
Before the modern A90 road was constructed, the pass served as one of the eight major crossing points for those travelling over the Grampians to Deeside and into Northern Scotland; this entire crossing trackway is historically known as the Cairnamounth. Deriving from this theory, a small village grew up in the pass. The high granite tor of Clachnaben overlooks the road (now called the B974 road) through the pass. The Scottish Tourist Board describes the modern B974 as an "adventurous" road, and it is often impassable due to snow or flooding in winter. In the summer fatalities are commonly reported in the press.