| A Band Apart | film production company | Los Angeles | 1991 |
| A. T. Cross Company | business, public company | Lincoln | 1846 |
| ABC-CLIO | book publisher, publishing house | Santa Barbara | 1953 |
| Abercrombie & Fitch | business, clothing store chain, public company | New Albany | 1892 |
| Abilene Christian University | church college, private not-for-profit educational institution, seminary | Abilene | 1906 |
| AbioMed | business, public company | Danvers | 1981 |
| About.com | media company, website | — | April 21, 1997 |
| Access Systems Americas | business | Reston | — |
| Ace Hardware | organization, business | Oak Brook | 1924 |
| Activision | video game publisher, video game developer, subsidiary company | Santa Monica | October 1, 1979 |
| Actors Studio | drama school | New York City | October 5, 1947 |
| Adam & Eve | pornography company, sex shop, pornographic film studio | Hillsborough | March 1971 |
| Addison-Wesley | book publisher, publishing house | Boston | 1942 |
| AddThis | social bookmarking, business | Vienna | 2006 |
| AdMob | software company, business | Mountain View | 2006 |
| Adobe | software company, type foundry, business, data controller, enterprise, public company | San Jose | February 28, 1982 |
| Advance Auto Parts | car parts shop chain, business, public company | Roanoke | 1932 |
| Advent International | business, private equity firm | Boston | 1984 |
| Aeronca | aerospace manufacturer | Cincinnati, Middletown | 1928 |
| Aetna | insurance company, business, enterprise, public company | Hartford | 1853 |
| Affirm Films | business | Culver City | 2008 |
| AGBO | production company | Los Angeles | March 27, 2015 |
| Ageia | business | Santa Clara | 2002 |
| Agilent Technologies | business, enterprise, public company | Santa Clara | 1999 |
| Ahwahnee Hotel | lodge | — | 1927 |
| AIGA | regulatory college, nonprofit organization, private press, professional association | New York City | 1914 |
| AIM alliance | joint venture, alliance | — | October 2, 1991 |
| Air Force Institute of Technology | staff college, engineering education | — | 1919 |
| Air Sunshine | airline | Fort Lauderdale | 1982 |
| Airbnb | website, business, hotel booking website, enterprise, public company | San Francisco | 2008 |
| Airtable | spreadsheet, website, business | San Francisco | 2012 |
| AK Press | book publisher, small press | Chico | 1987 |
| Aksys Games | business | Torrance | July 14, 2006 |
| Alamo Rent a Car | business | Clayton | 1974 |
| Alaska Railroad Corporation | national railway, Class II railroad | Anchorage | 1914 |
| Albemarle Corporation | business, enterprise, public company | Baton Rouge | 1994 |
| Albert Einstein College of Medicine | university, organization | — | 1955 |
| Albertsons | supermarket chain, business, enterprise, public company | Boise | 1939 |
| Albertus Magnus College | private not-for-profit educational institution, school | — | 1925 |
| Alcon Entertainment | business, enterprise | Los Angeles | 1997 |
| Alcorn State University | historically black college or university, public educational institution of the United States, school, university, census-designated place in the United States, land-grant university | — | 1871 |
| Allen-Bradley | business, public company | Milwaukee | 1903 |
| AllianceBernstein | business, enterprise, public company | Nashville | 1967 |
| Alliant Techsystems | enterprise, public company, aerospace manufacturer | Arlington County | 1990 |
| Allis-Chalmers | business | Milwaukee | 1901 |
| Allison Engine Company | business | Indianapolis | 1915 |
| Allstate | business, enterprise, public company | Northbrook | April 17, 1931 |
| Ally Financial | bank, business, enterprise, credit institution, public company | Detroit, New York City | 1919 |
| Alpha Tomo Global Resoures Sdn Bhd | business, temporary work agency, enterprise, public company | Milwaukee | 1948 |
| Amazon Robotics | business | Massachusetts | January 1, 2003 |
| Amazon Web Services | platform as a service, hyperscaler, internet hosting service, computing platform, business | Seattle | March 2006 |
| Amblin Entertainment | television production company, animation studio, film production company | Universal City | 1981 |
| Amblin Television | business | Universal City | July 31, 1984 |
| AMC Global Media | public company | New York City | 1980 |
| Amdahl Corporation | business | Sunnyvale | October 19, 1970 |
| Ameren | holding company, public company | St. Louis | 1997 |
| America West Airlines | airline | Tempe | 1981 |
| American Academy in Rome | nonprofit organization, educational institution, research center | Rome, New York City | 1894 |
| American Academy of Arts and Sciences | nonprofit organization, learned society, academic publisher | Cambridge | May 4, 1780 |
| American Airlines | airline, public company | Fort Worth | April 15, 1926 |
| American Antiquarian Society | research library, nonprofit organization, historical society, learned society | Worcester | 1812 |
| American Association for the Advancement of Science | nonprofit organization, open-access publisher, international organization, academic publisher | Washington, D.C. | September 20, 1848 |
| American Association of Petroleum Geologists | voluntary association, academic publisher | — | 1907 |
| American Concrete Institute | organization, academic publisher | Farmington Hills | 1904 |
| American Conservatory Theater | theatre company, nonprofit organization, private not-for-profit educational institution | San Francisco | 1965 |
| American Cyanamid | business | Wayne | 1907 |
| American Eagle Outfitters | business, brick and mortar, public company | Pittsburgh | 1977 |
| American Economic Association | organization, open-access publisher, scientific society | Nashville | 1885 |
| American Geophysical Union | nonprofit organization, open-access publisher, scientific society | Washington, D.C. | 1919 |
| American Hockey League | professional sports league | — | 1936 |
| American Institute of Aeronautics and Astronautics | professional society, academic publisher | Reston | 1963 |
| American LaFrance | business, enterprise | Summerville | 1873 |
| American Library Association | nonprofit organization, open-access publisher, professional association, library association, academic publisher | Chicago | October 6, 1876 |
| American Locomotive Company | business | Schenectady, New York City | June 24, 1901 |
| American Numismatic Association | nonprofit organization, library, learned society | Colorado Springs | 1891 |
| American Physical Society | nonprofit organization, publishing house, open-access publisher, scientific society, learned society | College Park | May 20, 1899 |
| American Psychological Association | regulatory college, nonprofit organization, publishing house, open-access publisher, professional association, school accreditor | Washington, D.C. | July 1892 |
| American Radiator Building | skyscraper, hotel | — | 1924 |
| American Society for Testing and Materials | standards organization, business, company, learned society | West Conshohocken | 1961 |
| American Society of Civil Engineers | engineering society, regulatory college, professional association, academic publisher | Reston | 1852 |
| American Society of Mechanical Engineers | engineering society, regulatory college, organization, academic publisher | New York City | 1880 |
| American Sociological Association | nonprofit organization, learned society, academic publisher | 1430 K Street | 1905 |
| American Type Founders | type foundry, business | Elizabeth | 1892 |
| American University | research university, private not-for-profit educational institution, private university | — | 1893 |
| Ameristar Jet Charter | airline | Dallas | 2000 |
| Ametek | public company | Berwyn | 1930 |
| Amgen | biopharmaceutical company, business, enterprise, public company | Thousand Oaks | 1980 |
| Amherst College | liberal arts college, private not-for-profit educational institution | — | 1821 |
| Amkor Technology | service provider, business, enterprise, public company | Tempe | 1968 |
| Amlogic | business | Santa Clara | 1995 |
| Ampex | brand, organization, business | Redwood City | 1944 |
| AMR Corporation | business, enterprise | Fort Worth | October 1, 1982 |
| Analog Devices | business, enterprise, public company | Norwood | 1965 |
| Ancestry.com Inc. | business, database | Lehi | 1983 |
| Andrew Christian | business | Hollywood | 2001 |
| Andrews University | church college, private not-for-profit educational institution, open-access publisher, private university | Berrien Springs | 1874 |
| Anduril Industries | business, enterprise | California | 2017 |
| Angelo State University | public educational institution of the United States, university | San Angelo | 1928 |
| Aniplex of America | business, enterprise | Santa Monica | 2005 |
| Annapurna Interactive | video game publisher, company | Los Angeles | December 1, 2016 |
| Annapurna Pictures | film production company, entertainment company | Los Angeles | 2011 |
| Annual Reviews | nonprofit organization, publishing house, academic publisher | San Mateo, Palo Alto | 1932 |
| Anthology Film Archives | cinematheque, movie theater, film archive | — | November 30, 1970 |
| Anthropic | technology company, business, benefit corporation | San Francisco | January 26, 2021 |
| APC by Schneider Electric | trademark, business, enterprise | West Kingston | 1981 |
| Apollo Computer | business | Chelmsford | 1980 |
| Apollo Group | business, enterprise, public company | Phoenix | 1973 |
| Appalachian State University | public educational institution of the United States, university | Boone | 1899 |
| Appian Way Productions | film production company | West Hollywood | 2004 |
| Apple Inc. | corporation, technology company, business, enterprise, public company | Cupertino | April 1, 1976 |
| Applebee's | franchisor, restaurant chain | Kansas City | November 19, 1980 |
| Applied Materials | business, enterprise, public company | Santa Clara | 1967 |
| Aramark | business, public company | Philadelphia | 1959 |
| Arby's | fast food restaurant chain, business | Sandy Springs | 1964 |
| ARCO | oil company, business, gas station chain, enterprise | Los Angeles | 1966 |
| Arctic Coal Company | mining company | Boston | 1906 |
| ArenaNet | video game developer, business, enterprise | Bellevue | 2000 |
| Arizona State University | public educational institution of the United States, university, open-access publisher | Tempe | 1885 |
| Arkham House | book publisher, publishing house | Sauk City | 1939 |
| ArmaLite | small arms manufacturing company | Geneseo | 1954 |
| Armand Hammer United World College of the American West | boarding school, academic institution | Montezuma | 1982 |
| ARP Instruments, Inc. | business, musical instrument manufacturing company | United States | 1969 |
| Arrow Air | airline | — | 1947 |
| Art Students League of New York | arts venue, art academy | 57th Street | 1875 |
| Artforum | publishing house, magazine | New York City | June 1962 |
| ArXiv | bibliographic database, website, preprint server, disciplinary repository, open science tool, online database | — | August 14, 1991 |
| Ashland Inc. | business, enterprise, public company | Covington | 1924 |
| Asia Pacific Airlines | airline | Guam | 1998 |
| ASM International | engineering society, publishing house, organization | ASM Headquarters and Geodesic Dome | 1913 |
| Aspen Music Festival and School | annual event, nonprofit organization, conservatory, music festival | — | 1949 |
| Aspyr | video game publisher, video game developer | Austin | 1996 |
| Association for Computing Machinery | regulatory college, publishing house, organization, open-access publisher, scientific society, learned society | New York City | September 15, 1947 |
| Association for the Advancement of Artificial Intelligence | regulatory college, publishing house, scientific society | Palo Alto | 1979 |
| Association of Universities for Research in Astronomy | consortium, open-access publisher | — | 1957 |
| AST Research | business | Irvine | 1980 |
| Astra | launch service provider, startup company, aerospace manufacturer | Alameda | 2005 |
| Astrophysics Data System | bibliographic database, data library, open-access repository | — | 1992 |
| ATA Airlines | airline | Indianapolis | 1973 |
| Atari Corporation | video game publisher, technology company, business | Sunnyvale | July 2, 1984 |
| Atari Games | video game publisher, video game developer | Milpitas | July 1984 |
| Atari, Inc. | video game publisher, video game developer | Sunnyvale | June 9, 1972 |
| Atari, Inc. | video game publisher, video game developer | New York City | February 1993 |
| Atari, Inc. | video game publisher | New York City | February 1993 |
| Atlas Obscura | publishing house, brand, online encyclopedia, database | Greenpoint | 2009 |
| Au Bon Pain | business | Boston | 1978 |
| Auburn Automobile | business | Auburn | 1900 |
| Aurora University | private not-for-profit educational institution, university | Aurora | 1893 |
| Austin Peay State University | public educational institution of the United States, university | — | 1927 |
| Automatic Data Processing | software company, business, enterprise, public company, accounting software | Roseland | 1949 |
| AutoNation | business, car dealership, public company | Fort Lauderdale | 1996 |
| AutoZone | car parts shop chain, public company | Memphis | 1979 |
| Avalon Hill | tabletop role-playing game publisher, board game publishing company | Baltimore, Renton | 1958 |
| Ave Maria University | private not-for-profit educational institution, university | — | 1998 |
| Avery Dennison | public company | Glendale | 1935 |
| AviaBellanca Aircraft | aerospace manufacturer | Alexandria | 1927 |
| Avis Budget Group | business, public company | Parsippany-Troy Hills | 2006 |
| Avnet | business, public company | Phoenix | 1921 |
| Avon Products Inc. | multi-level marketing company, public company | New York City | 1886 |
| Awty International School | school, private school | — | 1956 |
| Axios | news website, business | Arlington County | 2017 |