| Abbreviation | Definition |
|---|---|
| IRPS | International Radiation Physics Society |
| IRRG | Ionising Radiations Research Group |
| ISBR | Inter-SubBand Radiation |
| ISE | Intensional Sequential Evaluator |
| ISE | Ion Selective Electrode |
| ISNAP | Institute for Structure and Nuclear Astrophysics |
| ISPI | International Summer Physics Institute |
| ISPP | Illinois State Physics Project |
| ISR | Initial State Radiation |
| ISS | Input to State Stability |
| ISSD | Isocyclic Stress-Strain Diagram |
| ISSP | Institute for Solid State Physics |
| ISSP | Institute Of Solid State Physics |
| ITAP | Isentropic Trajectory Analysis Project |
| ITBS | Imaging Technologies in Biomedical Sciences |
| ITD | Inlet Temperature Difference |
| ITER | International Thermonuclear Experemental Reactor |
| ITER | International Thermonuclear Experimental Reactor |
| ITGR | Interstitial Time Generation Ring |
| ITOP | Improving the Teaching of Physics |