| J2EE | Java 2 Platform, Enterprise Ediction |
| JAAS | Java Authentication and Authorization Service |
| JASD | Joint Agency Satellite Division |
| JAXA | Japan Aerospace Exploration Agency |
| JCL | Joint Cost Schedule Confidence Level |
| JCSDA | Joint Center for Satellite Data Assimilation |
| JDBC | Java Database Connectivity |
| JHSL | Johns Hopkins Spectral Library |
| JHT | Joint Hurricane Testbed |
| JIMAR | Joint Institute for Marine and Atmospheric Research |
| JISAO | Joint Institute for the Study of the Atmosphere and Ocean |
| JMA | Japan Meteorological Agency |
| JMS | Java Messaging Service |
| JMX | Java Maintenance Extensions |
| JNI | Java Native Interface |
| JOFOC | Justification for Other than Full and Open Competition |
| JPA | JAVA Persistence API |
| JPDO NextGen | Joint Planning Development Office - Next Generation Air Transportation Control System |
| JPEG | Joint Photographic Experts Group |
| JPL | Jet Propulsion Laboratory (NASA) |
| JPRT | Joint Program Review Team |
| JPSS | Joint Polar Satellite System (NOAA) |
| JRE | Java Runtime Environment |
| JTWC | Joint Typhoon Warning Center |
| JVM | Java Virtual Machine |
| JWST | James Webb Space Telescope |