| UAPT | Union of African Post- and Telecommunication |
| UHF | Ultra High Frequency (300 to 3000 MHz) |
| UIC | International Union of Railways |
| ULP-AID | Ultra Low Power Animal Implant Devices |
| UMTS | Universal Mobile Telecommunication System (= FPLMTS) |
| UNESCO | United Nations Education, Scientific and Cultural Organization |
| UNO | United Nations Organization |
| URSI | Union Radio Scientifique International |
| USAT | Ultra-Small Aperture Terminals |
| UT | Universal Time |
| UTC | Coordinated Universal Time |
| UTRA | UMTS Terrestrial Radio Access |
| UWB | Ultra Wide Band |