| Lucasfilm Animation | business, enterprise | San Francisco | May 12, 2003 |
| Lucasfilm Games | video game publisher, video game developer | San Francisco, Letterman Digital Arts Center | May 1982 |
| LuckyChap Entertainment | film production company | Los Angeles | — |
| Lulu Press, Inc. | self-publishing company, publishing house, website | Raleigh | 2002 |
| Lycoming | business | Williamsport | 1845 |
| Lycos | enterprise, university spin-off | Waltham | 1994 |
| M&T Bank | bank, business, financial institution, public company | Buffalo | 1856 |
| Macalester College | private not-for-profit educational institution, liberal arts college in the United States | — | 1874 |
| Mack Trucks | business, enterprise | Allentown, Greensboro | 1900 |
| Magnolia Pictures | film production company, film distributor | Dallas | 2001 |
| Magpul | business | — | — |
| MakerBot Industries | business, enterprise | New York City | January 20, 2009 |
| Mannes College The New School for Music | conservatory | — | 1916 |
| Mapbox | software company, startup company | Washington, D.C. | 2010 |
| Marine Corps University | naval force university, staff college, university | — | 1989 |
| Marmot | business, enterprise | Santa Rosa | 1974 |
| Marquis Who's Who | publishing house | Berkeley Heights | 1899 |
| Marriott International | hotel chain, business, enterprise, public company | Bethesda | October 8, 1993 |
| Martin Marietta | business, enterprise | Bethesda | 1961 |
| Marvel Studios | film production company | Burbank | 1993 |
| MarVista Entertainment | privately held company | Los Angeles | 2003 |
| Mary Kay | multi-level marketing company | Dallas | 1963 |
| Masdar | business | Abu Dhabi | April 2006 |
| Massachusetts College of Art and Design | public educational institution of the United States, art academy, higher education institution | — | 1873 |
| Masten Space Systems | business | Mojave | 2004 |
| Mastercard | organization, business, card association, enterprise, public company, payment system | Purchase | 1966 |
| Match Group | business, company, public company | Kerrville | 2009 |
| Matson, Inc. | business, public company | Honolulu | 1882 |
| Max's Kansas City | restaurant, nightclub, music venue | — | 1965 |
| Maxwell Technologies | business | San Diego | 1965 |
| Mayo Clinic | nonprofit organization, clinic, educational institution, research institute | Rochester | 1889 |
| Maytag | business, subsidiary company | — | 1893 |
| MCA Inc. | media company, entertainment company, conglomerate, company, public company | Chicago | November 10, 1958 |
| McDonnell Aircraft Corporation | aerospace manufacturer | St. Louis | July 6, 1939 |
| McDonnell Douglas | former entity, defense contractor, aerospace manufacturer | St. Louis | 1967 |
| McIntosh Laboratory | business, enterprise | Binghamton, New York City | 1949 |
| Mead Johnson | business, enterprise, public company | Glenview | 1905 |
| Meijer | supermarket chain, gas station chain | Grand Rapids | 1934 |
| Memorex | brand, business | Cerritos | 1961 |
| Mentholatum | business | Orchard Park | 1889 |
| Mentor Graphics | business, enterprise, public company | Wilsonville | 1981 |
| Merchant Ivory Productions | film production company | London | 1961 |
| Merck & Co. | pharmaceutical company, business, enterprise, public company | Rahway | 1891 |
| Meredith Corporation | media conglomerate, business, public company | Des Moines | 1902 |
| Meritor | public company | Troy | 1997 |
| Merrell | business | Rockford | 1981 |
| Merrill | business, enterprise, credit institution | New York City | January 6, 1914 |
| Mesa Airlines | regional airline | Phoenix | 1980 |