Keystone may refer to:
- Keystone (architecture), a central stone or other piece at the apex of an arch or vault
- The keystone effect, caused by projecting an image onto a surface at an angle, or by photography at an angle
- Keystone (cask), a wooden or plastic fitting used in ale casks
- Keystone module, a type of data connector mounted in walls and patch panels
- Keystone species, species that have a larger effect on their environment than is purely due to their abundance
- Operation Keystone during World War II
- The Keystone asterism in the Hercules constellation
- Keystone Press Awards, given to Pennsylvania reporters
- Keystone (limestone), a type of limestone quarried in the Florida Keys
- Keystone, a variety of slotted screwdriver blade
- Keystone Initiative, a medical protocol to reduce infection rates
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