Flanders Moss (Scottish Gaelic: A’ Mhòine Fhlànrasach) is an area of raised bog lying in the Carse of Forth in west Stirlingshire, Scotland. The villages of Thornhill and Port of Menteith lie to the north with the villages of Kippen and Buchlyvie lying to the south. The moss is a National Nature Reserve, managed by NatureScot. Formed on the Carse of Stirling over 8000 years ago, it is an internationally important habitat currently undergoing active restoration. The eastern part of Flanders Moss is the largest raised bog in Europe to remain in a predominantly near-natural state.

As well as being an important habitat for wildlife, Flanders Moss also plays a key role for carbon sequestration acting as a carbon sink.

The bog is composed of an underlayer of sphagnum mosses, on top of which grows heather, cross-leaved heath and cotton-grass. Core samples from the peat show that there were very few trees on the bog for most of its life, however trees and scrub have spread over around 200 ha: these are predominantly birch, although Scots pine and the non-native rhododendron can also be found. The moss supports many plant species that are specialised to boggy conditions, including round-leaved sundew, cranberry, bog asphodel, white beak-sedge, and the nationally scarce bog rosemary.

The bog is home to many species of invertebrates, especially moths: 215 species of moth have been recorded here, including rare species such as Lampronia fuscatella and the Rannoch brindled beauty. Many of the invertebrate are associated with the trees and scrub on the bog. Bird species known to breed at Flanders Moss include snipe, curlew and stonechat on the open parts of the moss, with tree pipit, cuckoo and wood warbler preferring the wooded areas. Winter visitors include whooper swans, and greylag and pink-footed geese. Raptors such as hen harriers, short-eared owls and ospreys can also be seen.

Red and roe deer are known to visit the reserve, and otters make use the network of ditches to pass through the area. Flanders Moss is also home to many species of both reptiles and amphibians. Reptile species include adders, common lizards, and slow worm.

The enclosure at Ballangrew on the western edge of the moss may have served as a hunting lodge during the mediaeval period. During the 18th and early 19th centuries objects dating from the Bronze Age to the Roman period were found in the vicinity of Ballangrew, including a Bronze Age cauldron made of beaten bronze.

There are a number of other archaeological sites surrounding the moss, many of which consist of ditches, peat banks and dams used to drain the land to improve it for agriculture. During the 18th century, drainage of the land was encouraged by the lawyer, historian and improver Henry Home, Lord Kames, but a substantial portion survived this development at two sites - West Flanders Moss and East Flanders Moss.

The Strathendrick and Aberfoyle Railway was built through West Flanders Moss. Opening in 1880, the line ran between the villages of Buchlyvie and Gartmore. In the 1970s, the rest of West Flanders Moss was drained and planted with a commercial forest by the Forestry Commission, though much of the plantation is now being removed and the moss restored to its natural state.