A millstone is a stone used in gristmills, for grinding wheat or other grains.

Millstone may also refer to:

• "Millstone", a song on Brand New's 2006 album The Devil and God Are Raging Inside Me
• "Millstone", a song on Eisley's 2013 album Currents
• The Millstone (novel), a novel by Margaret Drabble

• Millstone Nuclear Power Plant, the only nuclear power generation site in Connecticut
• Millstone River, a 38.6-mile-long (62.1-kilometer) tributary of the Raritan River in central New Jersey
• Millstone Township, New Jersey, a township in Monmouth County, New Jersey, United States
• Millstone, Mercer County, New Jersey, an unincorporated community located within East Windsor Township in Mercer County, New Jersey, United States
• Millstone, New Jersey, a borough in Somerset County, New Jersey, United States

• James Millstone (1930–1992), American journalist and editor
• Millstone Coffee, a brand of coffee sold in the US
• Millstone Grit, any of a number of coarse-grained sandstones of Carboniferous age which occur in the British Isles
• Millstone Hill, a fully steerable dish antenna

• Grindstone, a round sharpening stone used for grinding or sharpening ferrous tools