| Acronym | Meaning |
| IOSH | Institution Of Occupational Safety And Health |
| IOSRR | Infinite Order Sudden Rigid-rotor Approximation |
| IOSVR | Infinite Order Sudden Vib-rotor Approximation |
| IOW | Integrated Optical Waveguide |
| IP | Inhalable Particle |
| IP | Impact Parameter Approximation |
| IP | Ionization Potential |
| IPA | International Pharmaceutical Abstracts |
| IPA | Independent-pair Approximation |
| IPA | Independent-particle Approximation (in Quantum Calcns. On Solids) |
| IPA | Inverted Perturbation Approach (in Mol. Potential-energy Curves Calcn.) |
| IPAA | Instrumental Photon Activation Analysis |
| IPAC | Infrared Processing And Analysis Center |
| IPAD | Integrated Pulsed Amperometric Detection |
| IPAN | Imaging Passive-active Neutron |
| IPC | Integrated Pollution Control |
| IPC | International Patent Classification |
| IPC | Ion-pair Chromatography |
| IPC | Ischemic Preconditioning |
| IPCC | Intergovernmental Panel On Climate Change |
| IPCM | Isodensity Polarizable Continuum Model [ab Initio Method] |
| IPCS | International Program On Chemical Safety |
| IPDA | Intensified Photodiode Arrays |
| IPDI | Isophorone Diisocyanate |
| IPEM | Ion-photon Emission Microscopy |
| IPES | Inverse Photoemission Spectroscopy |
| IPF | Inorg. Polymer Flocculant |
| IPG | Immobilized PH Gradient |
| IPHAS | The INT/WFC Photometric H-alpha Survey Of The Northern Galactic Plane |
| IPIB | Intense Pulsed Ion Beam |
| IPIC | Intellectual Property Institute Of Canada |
| IPIECA | International Petroleum Industry Environmental Conservation Association |
| IPIRDW | Independent-process (and) Isolated-resonance (approxn. Using) Distorted Waves |
| IPM | Independent Particle Model |
| IPM | Integrated Pest Management |
| IPMA | Ion Probe Microanalysis |
| IPMI | International Precious Metals Institute |
| IPMS | Infinite Periodic Minimum Surfaces |
| IPN | Interpenetrating Polymer Network |
| IPNO | Independent-pair Natural Orbital |
| IPNS | Intense Pulsed Neutron Source |
| IPNSO | Independent-pair Natural Spin Orbital |
| IPOD | International Phase Of Ocean Drilling |
| IPP | Isotactic Polypropylene |
| IPPA | Independent Pair-potential Approximation |
| IPPC | Integrated Pollution Prevention And Control |
| IPPP | Inner Projections (of The) Polarization Propagator (in Calcns. On Nuclear Spin Coupling) |
| IPPP | Isopropylphenyl Phosphate |
| IPPP | Iterative Pariser-Parr-Pople Method |
| IPS | Inclined Plate Settler (for Wastewater Treatment) |