| Perseus Digital Library | digital library | — | 1987 |
| Petco | pet store chain, business | San Diego | 1965 |
| PetSmart | pet store chain, business | Phoenix | 1986 |
| PGA Tour Champions | professional golf tour | — | 1980 |
| Philip Morris International | organization, business, enterprise, public company | Stamford, Lausanne | 1987 |
| Phillips Academy | boarding school, school, high school | — | April 1778 |
| Phillips Exeter Academy | boarding school, private school, university-preparatory school, first school, primary school | — | 1781 |
| Phillips Petroleum Company | business | Bartlesville | 1917 |
| Picsart | software company | San Francisco | January 1, 2011 |
| Pierce-Arrow | business, automobile manufacturer | Buffalo | 1870 |
| PIMCO | business | Newport Beach | 1971 |
| Pinkberry | restaurant chain, business | Los Angeles | 2005 |
| Pinnacle Systems | business | Mountain View | 1986 |
| Pioneer Hi-Bred | business, enterprise | Johnston | 1926 |
| Plan B Entertainment | film production company | Los Angeles | 2002 |
| Planet Labs | business, public company | San Francisco | December 28, 2010 |
| Platinum Dunes | film production company | Los Angeles | 2001 |
| Playboy Enterprises | business, enterprise | Los Angeles | 1953 |
| Playgirl | pornographic film studio, magazine | — | 1973 |
| Playtone | television production company, film production company | Santa Monica | January 23, 1998 |
| Plaza Hotel | skyscraper, tower block, hotel, workplace | — | 1907 |
| PNC Financial Services | bank, business, enterprise, credit institution, public company | One PNC Plaza | 1982 |
| PNY Technologies | business, enterprise | Parsippany-Troy Hills | 1985 |
| Polar Air Cargo | airline | Purchase | 1993 |
| Polaris | motorcycle manufacturer, enterprise, automobile manufacturer, public company | Medina | 1954 |
| Polycom | business, enterprise, public company | San Jose | 1990 |
| 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 |
| Portland State University | public educational institution of the United States, university, open-access publisher | — | 1946 |
| Powell Peralta | business | — | 1978 |
| Powell's Books | book vendor, bookstore chain, business | Portland | 1971 |
| Powerset | business | San Francisco | 2005 |
| PR Newswire | information resource, business | Manhattan | March 8, 1954 |
| Prairie View A&M University | historically black college or university, public educational institution of the United States, university, land-grant university | — | 1876 |
| Pratt & Whitney | business | East Hartford | 1925 |
| Pratt Institute | private not-for-profit educational institution, private university | New York City | 1887 |
| Precision Manuals Development Group | business, enterprise | Alexandria | 1997 |
| Prezi | startup company, computing platform | San Francisco | April 2009 |
| Principal Financial Group | business, enterprise, public company | Des Moines | 1879 |
| Pro Wrestling Guerrilla | business | Southern California | 2003 |
| Proactiv Solution | business | — | 1995 |
| Project MUSE | digital library | — | 1995 |
| ProQuest | privately held company, online database | Ann Arbor | 1938 |
| Providence College | private not-for-profit educational institution, university | — | 1917 |
| Providence Equity Partners | business, enterprise | 50 Kennedy Plaza | 1989 |
| PSA Airlines | airline | Dayton | 1980 |
| Psychology Today | media company, website, magazine | New York City | 1967 |