| American Tourister | brand, business | Rhode Island | 1933 |
| American Type Founders | type foundry, business | Elizabeth | 1892 |
| American University | research university, private not-for-profit educational institution, private university | — | 1893 |
| American University of the Caribbean | university | Coral Gables | 1978 |
| American Wrestling Association | business, enterprise | Minneapolis | 1960 |
| American Zoetrope | production company, film production company | San Francisco | 1969 |
| Ametek | public company | Berwyn | 1930 |
| Amgen | biopharmaceutical company, business, enterprise, public company | Thousand Oaks | 1980 |
| Amkor Technology | service provider, business, enterprise, public company | Tempe | 1968 |
| Amoco | oil company | Chicago | 1889 |
| Amplifon | public company | Milan | 1950 |
| Amway | multi-level marketing company | Michigan | November 9, 1959 |
| Analog Devices | business, enterprise, public company | Norwood | 1965 |
| Anchor Brewing Company | brewery, business | San Francisco | 1896 |
| AND1 | manufacturing company, subsidiary company | Aliso Viejo | 1993 |
| Angel Studios | production company, streaming media, video streaming service | Provo | March 25, 2021 |
| 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 |
| Annual Reviews | nonprofit organization, publishing house, academic publisher | San Mateo, Palo Alto | 1932 |
| Anonymous Content | television production company, film production company | Culver City | 1999 |
| Anschutz Entertainment Group | business | Los Angeles | — |
| Anthology Film Archives | cinematheque, movie theater, film archive | — | November 30, 1970 |
| Anthropic | technology company, business, benefit corporation | San Francisco | January 26, 2021 |
| Anti- | independent record label | Los Angeles | 1999 |
| 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 |
| Apple Store | shop, electronics store chain | — | May 19, 2001 |
| Applebee's | franchisor, restaurant chain | Kansas City | November 19, 1980 |
| Archegos Capital Management | business | Manhattan | October 9, 2001 |
| Archie Comics | comics publishing company, book publisher, business | New York, Pelham | 1939 |
| Arctic Coal Company | mining company | Boston | 1906 |
| ArenaNet | video game developer, business, enterprise | Bellevue | 2000 |
| Aria Resort and Casino | skyscraper, casino, hotel | — | 2009 |
| Arista Networks | business, public company | Santa Clara | October 2004 |
| Arkham House | book publisher, publishing house | Sauk City | 1939 |
| ArmaLite | small arms manufacturing company | Geneseo | 1954 |
| ARP Instruments, Inc. | business, musical instrument manufacturing company | United States | 1969 |
| Arquitectonica | interior decoration firm, architectural firm | Miami | 1977 |
| Arrow Air | airline | — | 1947 |
| Art Institute of Chicago | nonprofit organization, educational institution, art museum | Chicago | 1879 |
| Art Students League of New York | arts venue, art academy | 57th Street | 1875 |
| Arthur D. Little | management consulting company | Brussels metropolitan area | 1886 |
| Arthur J. Gallagher & Co. | business, public company | Itasca | 1927 |
| ArXiv | bibliographic database, website, preprint server, disciplinary repository, open science tool, online database | — | August 14, 1991 |
| Ashland Inc. | business, enterprise, public company | Covington | 1924 |