Grain mill, flour mill or cereal mill, can refer to both the building where the grain is ground and the grinding mechanism.

The Greek geographer Strabo already reported in his work Geography about the existence of water-powered mills that ground grains in Cabira, Asia Minor (Turkey) around 71 BC. C.[1]​.

The old water mills had horizontal paddle wheels. The paddle wheel was attached to an axle which, in turn, was attached to the center of a millstone called a running stone. The turning force produced by the water in the paddles was transferred directly to the sliding stone, causing it to grind against a static stone beneath the first. It had the disadvantage that the speed of rotation of the stone was dependent on the volume and flow of water available and was therefore only suitable for use in mountainous regions with fast-flowing rivers. This dependence on the volume and flow rate of water also meant that the speed of rotation of the stone was highly variable and the optimal grinding speed could not always be maintained.

Vertical wheels were used during the Roman Empire from the end of the first century AD and were described by Vitruvius. Watermills continued to be used until the end of the year 1000 and even beyond in some cases.

The first flour windmill was built in present-day Afghanistan, Pakistan and Iran around the 19th century.[3]​.

Modern mills typically use electricity or fossil fuels to rotate parts, such as rollers, made of steel or cast iron to separate the inner part of the grain from the bran. Different grinding techniques produce visibly different results. Stone-ground flour is often preferred by bakers for its better texture and flavor, in addition to having better baking qualities.[4] It has been argued that with stone grinding, which is slower than with metals, the flour does not heat up as much and the grain fat does not oxidize as quickly (due to beta oxidation) and does not easily become rancid, in addition to better preserving some vitamins such as thiamine.

Modern grain mills only grind grain clean of impurities (without chaff or other debris or impurities), but historically some grain mills had facilities for cleaning and sieving grain.