Keystone

• Keystone (architecture), the 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 correction for these types of distortion

Business

• Keystone Aircraft Corporation, an early manufacturer of airplanes
• Keystone (beer brand), a beer from Coors Brewing Company
• Keystone Camera Company
• Keystone View Company, a US photo agency founded in 1892
• Keystone (1899 automobile), a steam car from Lebanon, Pennsylvania
• Keystone (1914 automobile), an automobile from Pittsburgh

Entertainment

• Keystone (video game), an Xbox Live Arcade casino gambling game
• Keystone Cops, a series of silent movies
• Keystone Kapers, a classic Atari game wherein a police officer pursues a thief
• Keystone Studios, movie studio

Places

• The "Keystone State", nickname for the U.S. Commonwealth of Pennsylvania, in use by 1802
• Keystone, Colorado, a town
• Keystone Resort, the related ski resort
• Keystone, Florida, an unincorporated community
• Keystone, Indiana
• Keystone, Iowa
• Keystone, Montana
• Keystone, Nebraska
• Keystone, South Dakota, a town near Mount Rushmore
• Keystone at the Crossing, a business/shopping district located in Indianapolis, Indiana
• The Fashion Mall at Keystone, a mall located in the Keystone shopping district
• Keystone Heights, Florida, a small cityFictional
• Keystone City, home of the comic book character the Flash

Railroads

• Keystone Service (Amtrak), Amtrak's current New York-Harrisburg
• Keystone (Amtrak), Amtrak's former New York-Pittsburgh service
• Keystone (PRR), Pennsylvania Railroad's former New York-Washington service

Schools

• Keystone School, a private K-12 school in San Antonio, Texas
• Keystone National High School, a private correspondence school

Other uses

• 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 Hercules (constellation)
• Keystone (limestone), a type of limestone quarried in the Florida Keys
• The keystone variety of slotted screwdriver blade