Mill stones are used in windmills and watermills for grinding wheat or other grains.

In Britain there are two types of mill stone:

• Derbyshire Peak stones of grey millstone grit, cut from one piece, used for grinding barley; disused Derbyshire Peak stones are used as decorative signposts at the boundaries of the Peak District National Park.

• French burr stones, used for finer grinding. Not cut from one piece, but built up from sections of quartz, cemented together, and bound with iron bands.

Not all windmills were used for grinding corn; many were used for drainage purposes and referred to as windpumps; they were not equipped with mill stones.