Keystone

Keystone or key-stone 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
 * 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), part of the Xbox Live Arcade title Fable 2 Pub Games
 * Keystone (band), led by jazz trumpeter Dave Douglas
 * 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

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 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"

Railroads

 * Keystone Corridor, a rail corridor from Philadelphia to Pittsburgh
 * Keystone Service, a current New York-Harrisburg service
 * Keystone (Amtrak train, 1979–1981), a predecessor of the current service
 * 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), 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
 * Keystone, an education program at the U.S. National Defense University

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
 * The Keystone, journal of the Pennsylvania Railroad Technical and Historical Society
 * The Keystone, Pennsylvania news website owned by Courier Newsroom