| Acronym | Meaning |
| NPO | National Program Office |
| NPOC | Nonpurgeable Organic Carbon |
| NPOE | 2-nitrophenyl Octyl Ether |
| NPOESS | National Polar Orbiting Environmental Satellite System |
| NPOX | Nonpurgeable Organic Halide |
| NPP | Net Primary Productivity |
| NPP | Nuclear Power Plant |
| NPPC | Nuclear Power Plant Consultant |
| NPR | Net Protein Retention |
| NPRA | National Petroleum Refiners Association |
| NPRI | National Pollutant Release Inventory |
| NPS | National Park Service (US) |
| NPS | Nonpoint Source |
| NPSO | Nonpaired Spatial Orbital |
| NPSSMO | Nonpaired Spin Spatial Molecular Orbital |
| NPTII | Neomycin-phosphotransferase II |
| NPTN | National Pesticide Telecommunications Network |
| NPTOC | Nonpurgeable Total Organic Carbon |
| NPV | Net Present Value {economics} |
| NPY | Neuropeptide Y |
| NQCC | Nuclear Quadrupole Coupling Constants |
| NQI | Nuclear Quadrupole Interaction |
| NQR | Nuclear Quadrupole Resonance |
| NRA | National Rivers Authority (UK) |
| NRA | Neutron Reaction Analysis |
| NRA | Nuclear Reaction Analysis (Rensselear Polytech) |
| NRAO | National Radio Astronomy Observatory |
| NRBC | Nucleated Red Blood Cells |
| NRC | National Research Council |
| NRC | National Response Center |
| NRC | Nuclear Regulatory Commission |
| NRCC | National Research Council Of Canada |
| NRD | Natural Resource Damage |
| NRDA | Natural Resource Damage Assessment |
| NRDAM | Natural Resource Damage Assessment Model |
| NRDC | Natural Resources Defense Council |
| NREL | National Renewable Energy Laboratory (formerly SERI) |
| NREP | National Registry Of Environmental Professionals |
| NRFE | Normalised Relative Fit Error |
| NRHF | Numerical Restricted Hartree-Fock |
| NRIOSA | Nonreactive Infinite-order Sudden Approxn. |
| NRL | Naval Research Laboratories |
| NRM | Natural Remanent Magnetization |
| NRM | Nuclear Reference Material |
| NRMA | Nonresonant Microwave Absorption |
| NRMPI | Non-resonant Multiphoton Ionization |
| NRMRL | National Risk Management Research Laboratory |
| NRMS | Neutralization-reionization Mass Spectrometry |
| NRO | Natural Reaction Orbital |
| NRPB | National Radiological Protection Board |