| 405 Ads, Inc. | California |
| 405 Group | California |
| 406 Ventures | Massachusetts |
| 40Billion.com, Inc. | Georgia |
| 410 Labs | Maryland |
| 410 Medical | North Carolina |
| 411 Locals | |
| 412 Venture Fund, L.P. | Pennsylvania |
| 42 Technologies, Inc. | California |
| 42, Inc. | California |
| 42.Ventures | Utah |
| 420 Web Pros | California |
| 425 Consulting Group, LLC | |
| 42Chat | Utah |
| 42connect | |
| 42DM | New Jersey |
| 42U.com | Colorado |
| 43North | New York |
| 44 Degrees North, LLC | Vermont |
| 44 Interactive | South Dakota |
| 44 North Credit Union | |
| 4490 Ventures | Wisconsin |
| 45 RPM Software | California |
| 451 Degrees | California |
| 451 Research, LLC | New York |
| 47 Degrees, LLC | Washington |
| 47Billion | |
| 48HoursLogo.com | Georgia |
| 490 BioTech, Inc. | Tennessee |
| 4AllThingsWeb.com | Tennessee |
| 4Blind | Massachusetts |
| 4byte4 | Washington |
| 4C Medical Technologies, Inc. | Minnesota |
| 4Catalyzer Corporation | Connecticut |
| 4COM, Inc. | Minnesota |
| 4Corners Creative, LLC | |
| 4D Healthware | Illinois |
| 4D Molecular Therapeutics | California |
| 4D Path, Inc. | Massachusetts |
| 4D Pipeline | |
| 4Discovery | Illinois |
| 4eGuru, Inc. | California |
| 4EVER Design Studio | Illinois |
| 4Front Technologies | California |
| 4G Capital | Maryland |
| 4G Clinical | Massachusetts |
| 4Geeks Academy, LLC | Florida |
| 4immune Therapeutics | |
| 4Inkjets | California |
| 4iQ.com | California |