| Acronym | Meaning |
| INDA | Investigational New Drug Application |
| INDC | International Nuclear Data Committee |
| INDO | Intermediate Neglect Of Differential Overlap |
| INDO/2-AHP | INDO/2-average Hole Potential |
| INDO/2-HP | INDO/2-hole Potential |
| INDO/CS | INDO/conformation Spectra |
| INDO/RZ | Intermediate Neglect Of Differential Overlap/Ridley-Zerner |
| INDO/S | INDO/spectroscopic Approxn. |
| INDO/S | Intermediate Neglect Of Differential Overlap Screened Approxn. |
| INDO/SP | Intermediate Neglect Of Differential Overlap/spin Polarization |
| INDOEX | Indian Ocean Experiment |
| INDOR | Internal Nuclear Double Resonance |
| INEEL | Idaho National Engineering And Environmental Laboratory |
| INEGA | Instituto Nacional De Estadistica |
| INEL | Idaho National Engineering Lab. |
| INEPT | Insensitive Nuclei Enhanced By Polarization Transfer |
| INFCE | International Nuclear Fuel Cycle Evaluation |
| INFERNO | Irradiation Of Narrow Frequency Envelopes By Repeated Nutation And Orbiting |
| INID | Internationally Agreed Numbers For The Identification Of Data |
| INIS | International Nuclear Information System |
| INMM | Institute Of Nuclear Materials Management |
| INMS | Institute For National Measurement Standards |
| INN | International Nonproprietary Names (for Drugs) |
| INO | Iterative Natural Orbital |
| INP | Initial Notification Plan |
| INPADOC | International Patent Documentation Center |
| INPI | The French National Institute Of Industrial Property |
| INQUA | International Association For Quaternary Research |
| INR | International Normalized Ratio |
| INRS | Institut National De Recherche Et De Securite (Paris |
| INS | Inelastic Neutron Scattering |
| INS | Ion Neutralization Spectroscopy |
| INSERM | Institut National De La Sante Et De La Recherche Medicale |
| INSIPID | Inadequate Sensitivity Improvement By Proton Indirect Detection |
| INSPEC | Information Service For Physics And Engineering Communities |
| INTECOL | The International Association Of Ecology |
| INTEGRAL | International Gamma-Ray Astrophysics Laboratory |
| INTERFACE II | Integrated Reliable Fault-Tolerant Control For Large Engines |
| IOA | International Ozone Association |
| IOC | Intergovernmental Oceanographic Commission |
| IOC | Inorganic Chemical |
| IOC-OMEGA | Inclusion Of Overlap Charges In Omega Technique |
| IODE | International Oceanographic Data/Information Exchange (IOC) |
| IODS | Identical Orbitals For Different Spins |
| IOHA | International Occupational Hygiene Association |
| IOM | Institute Of Occupational Medicine |
| IOMC | Inter-Organization Program For The Sound Management Of Chemicals |
| IOS | Infinite Order Sudden Approximation |
| IOS-BS | Infinite Order Sudden-breathing Sphere |
| IOSA | Infinite Order Suden Approxn. (for Mol. Scattering Calcns.) |