| Acronym | Meaning |
| ISS | Ion Scattering Spectroscopy |
| ISSC | International Subcommission On Stratigraphic Classification |
| ISSI | International Society For Scientometrics And Informetrics |
| ISSJ | International Scientific Station Of The Jungfraujoch (atm. Observatory |
| ISSN | International Standard Serial Number |
| ISST | International Subcommission On Stratigraphic Terminology |
| IST | Internal Standardization Technique |
| ISTEA | Intermodal Surface Transportation Efficiency Act |
| ISTH | International Society On Thrombosis And Hemostasis |
| ISTO | Industry Standards And Technology Organization |
| ISTP | Index To Scientific And Technical Proceedings |
| ISTP | International Solar Terrestrial Physics |
| ISTS | Impulsive Stimulated Thermal Scattering [a Laser-based Ultrasonic Technique] |
| ISV | In Situ Vitrification |
| ISV | Initial Settling Velocity |
| ISVM | Iterative Schwinger Variational Method |
| ISVS | In Situ Vapor Stripping |
| ISWMP | Integrated Solid Waste Management Plan |
| ISX | Impurity Study Expt. |
| ISX | Insoluble Starch Xanthate (ion Exchanger For Wastewater Treatment) |
| IT | Integral Transform |
| ITAM | Immunoreceptor Tyrosine-based Activation Motif |
| ITC | Interagency Testing Committee (TSCA) |
| ITC | International Translation Center |
| ITC | Ionic Thermal Currents |
| ITC | Isothermal Titration Calorimetry |
| ITCZ | Intertropical Convergence Zone (of Seawater) |
| ITD | Ion Trap Detector (mass Spectrometry) |
| ITDHO | Improved Time-dependent Harmonic Oscillator |
| ITEP | Institute For Theoretical And Experimental Physics |
| ITER | International Thermonuclear Experimental Reactor |
| ITER | International Toxicity Estimates For Risk |
| ITFA | Iterative Target Factor Analysis |
| ITFM | Intergovernmental Task Force On Monitoring |
| ITFW | Improved Thomas-Fermi-Weizaecker (model) |
| ITG | Ion Temperature Gradient |
| ITIES | Interface Between Two Immiscible Electrolyte Solutions |
| ITMS | Ion Trap Mass Spectrometer |
| ITO | Indium Tin Oxide (gas Sensor |
| ITP | Inosine 5'-triphosphate |
| ITPOT | Improved Two-parameter Omega Technique |
| ITRC | Interstate Technology And Regulatory Cooperation Working Group |
| ITRI | Inhalation Toxicology Research Institute |
| ITRM | Inverse Thermoremanent Magnetization |
| ITRS | International Technology Roadmap For Semiconductors |
| ITS | Inelastic Tunnelling Spectroscopy |
| ITS | Internal Transcribed Spacer |
| ITT | Impact Transition Temperature |
| ITTFA | Iterative Target Transformation Factor Analysis |
| IU | International Unit |