| Acronym | Meaning |
| RDPV | Reverse Differential-pulse Voltammetry |
| RDQ | Reduced-dimensionality Quantum (calcn. Method) |
| RDS | Raman Difference Spectroscopy |
| RDS | Reflectance-difference Spectroscopy |
| RDS | Respiratory Distress Syndrome |
| RDW | Relativistic Distorted Wave |
| RDX | Royal Demolition Explosive |
| RE | Recoupled States (in Orbiting Resonances Calcns. In Atom-mol. Inelastic Scattering) |
| RE | Relativistic Eikonal |
| REA | Relaxed Eddy Accumulation |
| REA | Restriction Endonuclease Anal. |
| REA | Retrospective Exposure Assessment |
| REA | Reactive Arthritis |
| REACCS | Reaction Access System |
| REACH | Registration |
| READS | Restriction Enzyme Analysis Of Differentially-expressed Sequences |
| REAPDOR | Rotational-echo Adiabatic-passage Double-resonance |
| RECA | Regional Energy Convergence Approxn. (in Total Energies Calcns.) |
| RECLAIM | Regional Clean Air Incentives Market |
| RECP | Relativistic Effective-core Potential |
| RECP-CVC | Relativistic Effective-core Potential With Core-valence Correlation |
| RED | Radiation Enhanced Diffusion |
| REDOR | Rotational Echo Double Resonance |
| REE | Rare Earth Element(s) |
| REELM | Reflected Electron Energy Loss Microscopy |
| REELS | Reflection Electron Energy-loss Spectroscopy |
| REES | Red Edge Excitation Shift |
| REFET | Ref. Field Effect Transistor |
| REIMEP | Regulation European Interlab. Measurement Evaluation Program |
| REL | Recommended Exposure Limit(s) |
| RELAX | Refrigerator Enhanced Laser Analyzer For Xenon |
| RELMA | Remote Laser Microanalysis |
| REM | Reservoir Eutrophication Model |
| REM | Rapid Eye Movement |
| REM | Reflection Electron Microscopy |
| REMCO | ISO Council Committee On Reference Materials |
| REMOTS | Remote Ecological Monitoring Of The Seafloor |
| REMPI | Resonance-Enhanced Multiphoton Ionization (for Mass Spectrometry) |
| REMS | Reflection Mass Spectrometry |
| REMUS | Remote Environmental Monitoring Units |
| REO | Rare Earth Oxide |
| REOM | Reduced Equations Of Motion (method In Mol.-scattering Calcns.) |
| REOS | Remote Electro-Optical Sensor |
| REP | Radiological Emergency Planning |
| REP | Relativistic Effective Potential |
| REP | Rotating Electrode Process |
| REPA | Resource And Environmental Profile Analysis |
| REPE | Resonance Energy Per Pi Electron |
| REPELS | Reemitted Positron Energy Loss Spectroscopy |
| RER | Rough Endoplasmic Reticulum |