| Acronym | Meaning |
| JANAF | Joint Army Navy Air Force |
| JAPIO | Japan Patent Information Organization |
| JAXA | Japan Aerospace Exploration Agency |
| JCAHO | Joint Commission On Accreditation Of Healthcare Organizations |
| JCAMP | Joint Committee On Atomic And Molecular Physical Data |
| JCBN | IUPAC-IUB Joint Commission On Biochemical Nomenclature |
| JCPDS | Joint Committee On Powder Diffraction Standards |
| JEIDA | Japan Electronic Industry Development Association |
| JEIP | Joint Emission Inventory Program |
| JERS | Japanese Earth Resources Satellite |
| JESS | Joint Expert Speciation System |
| JESSI | Joint European Submicron Silicon Initiative |
| JET | Joint European Torus |
| JEV | Japanese Encephalitis Virus |
| JFCA | Japan Fine Ceramics Association |
| JFET | Junction Field-effect Transistor |
| JGOFS | Joint Global Ocean Flux Study |
| JI | Joint Implementation [with Regard To Greenhouse Gas Emission Redn.] |
| JICST | Japanese Information Center Of Science And Technology |
| JIMO | Jupiter Icy Moons Orbiter |
| JIPID | Japanese International Protein Information Databank |
| JIS | Japan Industrial Standard |
| JISC | Japanese Industrial Standards Committee |
| JJT | Josephson Junction Transistor |
| JKR | Johnson-Kendall-Roberts Contact Model |
| JME | Juvenile Myoclonic Epilepsypar |
| JME | Java Molecular Editor |
| JMTR | Japan Material Testing Reactor |
| JNK | C-Jun N-terminal Kinase |
| JOFET | Josephson Field Effect Transistor |
| JOIDES | Joint Oceanographic Institutions For Deep Earth Sampling |
| JOSO | Joint Organization For Solar Observations |
| JPCRD | Journal Of Physical And Chemical Reference Data |
| JPDR | Japan Power Demonstration Reactor |
| JPEG | Joint Photographic Expert Group |
| JPL | Jet Propulsion Laboratory |
| JPO | Japanese Patent Office |
| JSAC | Japan Society For Analytical Chemistry |
| JSGA | Japanese Spaceguard Association |
| JSMS | Japan Society Of Materials Science |
| JSR | Jet-stirred Reactor |
| JTU | Jackson Turbidity Unit |
| JULIC | Juelich Isochronous Cyclotron |
| JURIS | Justice Retrieval And Inquiry System |
| JWF | Jastrow Wave Function |
| JWKB | Jeffreys-Wentzel-Kramers-Brillouin (scattering Potential) |
| KADP | Kentucky Acid Deposition Program |
| KAERI | Korea Atomic Energy Research Institute |
| KAM | Kolmogorov-Arnold-Moser (theorem In Quantum Stochasticity) |
| KASIMA | Karlsruhe Simulation Model Of The Middle Atmosphere |