Sarsen stones are sandstone blocks found on Salisbury Plain and elsewhere. They are the remains of a cap of tertiary sandstone which once covered much of southern England. Natural sarsen boulders created by glacial and periglacial effects can be sometimes found scattered on the surface and the stone is also present in the surviving outcrops of the rock.

The builders of Stonehenge, Avebury and many other megalithic monuments in southern England chose to build with sarsen stones.

Several colourful etymologies exist for the name. It may be a mediaeval corruption of Saracen denoting the pagan significance of sarsen standing stones. Others have suggested Sanskrit links.

From the middle ages until the nineteenth century sarsen megaliths in Europe were a target for destruction by both religious zealots and commercial enterprise. The stones were sometimes toppled, cleared from fields under cultivation or broken up for reuse. Fire or explosives could be used to fracture or destroy the stone for use in buildings. Sarsen is not an ideal building material however, William Stukeley wrote that Sarsen is "always moist and dewy in winter which proves damp and unwholesome, and rots the furniture." In the case of Avebury the investors who backed the scheme to recycle the stone were bankrupted when the houses they built proved to be unsaleable and also prone to burning down.