| P. F. Chang's China Bistro | restaurant chain | — | 1993 |
| P.A. Semi | business | Santa Clara | 2003 |
| Pace University | private not-for-profit educational institution, university | New York City | 1906 |
| Pacific Data Images | business | Redwood City | 1980 |
| Pacific Southwest Airlines | airline | San Diego, California | 1949 |
| Packard Bell | technology company, brand, business, enterprise | Chatsworth | 1926 |
| Padlet | business, enterprise | San Francisco | December 1, 2012 |
| Palace Hotel | hotel | — | 1875 |
| Palantir Technologies | defense contractor, business, enterprise, public company | Miami | 2003 |
| Palm, Inc. | business, enterprise | Sunnyvale | 1992 |
| Palms Casino Resort | skyscraper, casino, resort | — | 2001 |
| Palo Alto Research Center | business | Palo Alto | 1970 |
| Pan Am | airline, business | New York City | March 14, 1927 |
| Pan American Health Organization | open-access publisher, international organization | Washington, D.C. | December 2, 1902 |
| Pandora | music streaming service, website, organization, recommender system, online music database, public company | Oakland | January 2000 |
| Panera Bread | restaurant chain, public company | Sunset Hills | 1987 |
| Panic | video game publisher, video game developer, business | Portland, Oregon | — |
| Pantene | brand, business | Switzerland | 1945 |
| Pantone | business, enterprise | Carlstadt | 1962 |
| Parallels | business, enterprise | Renton | 1999 |
| Paramount Global Content Distribution | business | Santa Monica, New York City | 1962 |
| Paramount Home Entertainment | film distributor, subsidiary company | Hollywood | 1975 |
| Paris Las Vegas | casino, hotel | — | September 1, 1999 |
| Parker Brothers | video game publisher, video game developer, board game publishing company, brand, business | Beverly, Salem | 1883 |
| Peabody Energy | business, enterprise, public company | St. Louis | 1883 |
| Peabody Institute | conservatory, school | Baltimore | 1857 |
| Peavey Electronics | business, enterprise | Meridian | 1965 |
| Pegasystems | business, public company | Cambridge | 1983 |
| Pei Wei Asian Diner | restaurant | Scottsdale | 2000 |
| PenAir | airline | Anchorage | 1955 |
| Pennsylvania Hospital | hospital, teaching hospital | — | May 11, 1751 |
| Pennsylvania State University | public research university | Penn State University Park | February 22, 1855 |
| Pennzoil | business, enterprise | Houston | 1963 |
| Penske Media Corporation | media company, business | Los Angeles | 2004 |
| Pentaho | business, software | Orlando | 2004 |
| People Incorporated | holding company, business, enterprise, public company | New York City | July 28, 1986 |
| Perdue Farms | business | Salisbury | 1920 |
| Perforce Zend | brand, business, enterprise | Minneapolis | 1999 |
| Perplexity AI | artificial intelligence website, organization, business | San Francisco | December 7, 2022 |
| Perry–Castañeda Library | academic library | — | 1977 |
| Perseus Digital Library | digital library | — | 1987 |
| Petroglyph Games | video game publisher, video game developer | Las Vegas | April 1, 2003 |
| PetSmart | pet store chain, business | Phoenix | 1986 |
| Phi Beta Kappa Society | organization, honor society, learned society, academic publisher | Washington, D.C. | December 5, 1776 |
| Phillips 66 | business, gas station chain, enterprise, public company | Westchase | May 1, 2012 |
| Phillips Exeter Academy | boarding school, private school, university-preparatory school, first school, primary school | — | 1781 |
| PhoenixEV | business, automobile manufacturer | Ontario, California | 2002 |
| Pi Studios | video game developer | Houston | 2002 |
| Piasecki Helicopter Corporation | former entity, aerospace manufacturer | Philadelphia | 1940 |
| Picturehouse | film production company, film distributor | New York City | 2005 |
| Piedmont Airlines | regional airline | Salisbury | 1948 |
| Pilgrim's Corp | business, public company | Greeley | 1946 |
| PIMCO | business | Newport Beach | 1971 |
| Pinkerton Government Services | private military company, private security company, business | Ann Arbor | February 1855 |
| Pinnacle Systems | business | Mountain View | 1986 |
| Pioneer Hi-Bred | business, enterprise | Johnston | 1926 |
| Piper Aircraft | aerospace manufacturer | Vero Beach Regional Airport, Florida, Vero Beach | 1927 |
| Pitney Bowes | business, enterprise, public company | Stamford | 1920 |
| Planetary Resources | space company, former entity, mining company | Seattle | January 1, 2009 |
| Plantronics | organization, business, public company | Santa Cruz | 1961 |
| PNC Financial Services | bank, business, enterprise, credit institution, public company | One PNC Plaza | 1982 |
| Polaris | motorcycle manufacturer, enterprise, automobile manufacturer, public company | Medina | 1954 |
| Pomona College | private not-for-profit educational institution, liberal arts college in the United States | Claremont | October 14, 1887 |
| Pope Manufacturing Company | automobile manufacturer | Hartford | 1876 |
| Populous | architectural firm | Kansas City | 1983 |
| Post University | private for-profit educational institution, university | — | 1890 |
| Powell Peralta | business | — | 1978 |
| Pratt & Whitney | business | East Hartford | 1925 |
| Pratt & Whitney Rocketdyne | business, subsidiary company | Canoga Park | 2005 |
| Pratt Institute | private not-for-profit educational institution, private university | New York City | 1887 |
| Praxair | business, enterprise | Danbury | 1907 |
| Precision Manuals Development Group | business, enterprise | Alexandria | 1997 |
| Prentice Hall | book publisher, publishing house | Upper Saddle River | 1913 |
| Prince Sports | business | Bordentown City | 1970 |
| Princess Cruises | business, cruise line | Santa Clarita | 1965 |
| Princeton School of Public and International Affairs | public policy school | — | 1930 |
| Princeton Theological Seminary | private not-for-profit educational institution, seminary | Princeton | 1812 |
| Princeton University | colonial colleges, research university, private not-for-profit educational institution, private university, academic publisher | Princeton | 1746 |
| Principal Financial Group | business, enterprise, public company | Des Moines | 1879 |
| Private Division | video game publisher | New York City | December 14, 2017 |
| Pro Wrestling Guerrilla | business | Southern California | 2003 |
| Proactiv Solution | business | — | 1995 |
| Product Red | business | New York City | 2006 |
| Progressive Corporation | insurance company, business, public company | Mayfield | March 10, 1937 |
| Providence College | private not-for-profit educational institution, university | — | 1917 |
| PRS Guitars | business | Stevensville | 1985 |
| PSA Airlines | airline | Dayton | 1980 |
| Psychology Today | media company, website, magazine | New York City | 1967 |
| Publix | supermarket chain, public company | Lakeland | December 27, 1921 |
| Punahou School | university-preparatory school | Honolulu | 1841 |