| 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 |