Keystone or key-stone or ''variation'', may refer to: * Keystone (architecture), a central stone or other piece at the apex of an arch or vault * Keystone (cask), a fitting used in ale casks

Business

* Keystone Law, a full-service law firm * Digital Keystone, a developer of digital entertainment software * Keystone Aircraft Corporation * Keystone Bridge Company, an American bridge building company * Keystone (beer brand) * Keystone Camera Company * Keystone (gasoline automobile) * Keystone (steam automobile) * Keystone Pipeline, a crude oil pipeline * Swiss Telegraphic Agency, Keystone-SDA/Keystone-ATS, a Swiss press agency * Keystone View Company, a US photo agency * Keystone (Berkeley, California), a defunct music club

Entertainment

* Keystone (video game), ''Keystone'' (video game), part of the Xbox Live Arcade title ''Fable 2 Pub Games'' * Keystone (band), led by jazz trumpeter Dave Douglas (trumpeter), Dave Douglas ** Keystone (album), ''Keystone'' (album), a 2005 album by the band * Keystone Cops, a silent movie series * ''Keystone Kapers'', a classic Atari game * Keystone Studios, a movie studio

Places

* The Keystone asterism in the Hercules (constellation), Hercules constellation

United States

* The "Keystone State", nickname for the U.S. Commonwealth of Pennsylvania * Keystone, Colorado, a town ** Keystone Resort, the related ski resort * Keystone, Florida, an unincorporated community * Keystone, Indiana * Keystone, Iowa * Keystone, Nebraska * Keystone, North Dakota * Keystone, Ohio * Keystone, South Dakota, a town near Mount Rushmore * Keystone, Wyoming * Keystone at the Crossing, a business/shopping district in Indianapolis, Indiana ** The Fashion Mall at Keystone, located in the Keystone shopping district * Keystone Heights, Florida * Keystone Canyon, Alaska * Keystone Lake, a resort area near Tulsa, Oklahoma * Keystone, Wisconsin

Canada

* The "Keystone Province", a List of provincial and territorial nicknames in Canada#Manitoba, nickname for the Province of Manitoba ** Keystone Centre, an arena and exhibition centre in Brandon, Manitoba

Fictional locations

* Keystone City, home of the comic book character The Flash * Keystone City, a holographic city in the ''Star Trek: The Next Generation'' episode "Emergence (Star Trek: The Next Generation), Emergence"

Railroads

* Keystone Corridor, a rail corridor from Philadelphia to Pittsburgh * ''Keystone Service'', a current New York-Harrisburg service **Keystone (Amtrak train, 1979-1981), ''Keystone'' (Amtrak train, 1979-1981), a predecessor of the current service * Keystone (Amtrak train, 1971-1972), ''Keystone'' (Amtrak train, 1971-1972), a former New York-Pittsburgh service operated by Amtrak * ''Keystone'', a former New York-Washington service operated by the Pennsylvania Railroad ** Keystone (train), ''Keystone'' (train), a lightweight train used for the service

Schools

* Keystone School, a private K-12 school in San Antonio, Texas, USA * Keystone National High School, a private correspondence school * Keystone Exam, a Pennsylvania standardized test

Sports

* Keystone Junior Hockey League, in Manitoba * Keystone Cup, Western Canadian Junior "B" ice hockey championship * Keystone (horse), a racehorse

Other uses

* Keystone (limestone), quarried in the Florida Keys * Keystone effect, caused by projecting an image onto a surface at an angle, or by photography at an angle * Keystone Initiative, a medical protocol to reduce infection rates * Keystone module, a type of data connector mounted in walls and patch panels * Keystone Press Awards * Keystone species, species that have a larger effect on their environment than is purely due to their abundance * Operation Keystone, during World War II * Keystone, a variety of screwdriver blade * "Keystone", a descriptive reference to the Book of Mormon