| Acronym | Meaning |
| RPMI | Roswell Park Memorial Institute |
| RPO | Resonant Periodic Orbit (on Potential Energy Surface In At. Or Mol. Scattering) |
| RPP | Renal Perfusion Pressure |
| RPP | Reverse Pulse Polarography |
| RPS | Reemitted Positron Spectroscopy |
| RPSA | Rapid Pressure Swing Adsorption |
| RPTP | Receptor Protein Tyrosine Phosphatase |
| RPV | Raccoon Parvovirus |
| RPV | Reactor Pressure Vessel |
| RPWBA | Relativistic Plane-wave Born Approximation |
| RPWBA-BC | RPWBA With Corrections For Increased Binding Energy And Coulomb Deflection |
| RQ | Reportable Quantity |
| RQ | Respiratory Quotient |
| RQCAR | Reportable Quantities For Carcinogens In Hazardous Waste |
| RQCISD | (spin) Restricted QCISD |
| RQDO | Relativistic Quantum Defect Orbital (method In Calcns. Of Oscillator Strengths) |
| RQTOX | Reportable Quantities For Chronically Toxic Hazardous Substances |
| RR | Relative Risk |
| RR | Round Robin (test) |
| RRC | Regional Response Center |
| RRDE | Rotating Ring Disk Electrode |
| RREL | Risk Reduction Engineering Laboratory |
| RRG | Rift-related Granitoids |
| RRGM | Recursive Residue Generation Method |
| RRHO | Rigid Rotor-harmonic Oscillator (approxn.) |
| RRIM | Reinforced Reaction-injection Molding |
| RRM | RNA Recognition Motif |
| RRM | Rayleigh-Ritz Method (for Quantum Calculations) |
| RRNA | Ribosomal Ribonucleic Acid |
| RRPA | Relativistic Random Phase Approximation |
| RRPA | Renormalized Random-phase Approxn. |
| RRPT | Registered Radiation Protection Technologist |
| RRR | Residual Resistivity Ratio |
| RRS | Resonance Raman Spectroscopy |
| RRS | Resonance Rayleigh Scattering |
| RRT | Regional Response Team |
| RRT | Relative Retention Time |
| RS | Rayleigh Schroedinger (perturbation Theory) |
| RS-HFPT | Rayleigh-Schroedinger Hartree-Fock Perturbation Theory |
| RS-LMTO-ASA | Real Space-linear Combination Of Muffin-tin Orbitals-atomic Sphere Approxn. |
| RSA | Rat Serum Albumin |
| RSA | Reverse Saturable Absorption |
| RSAC | Remote Sensing Applications Center (US Forest Service) |
| RSC | Risk Specific Concentration |
| RSC | The Royal Society Of Chemistry |
| RSC | Relative Source Contribution |
| RSC | Residual Sodium Carbonate |
| RSCA | Relativistic Semiclassical Approximation (for At. Scattering) |
| RSCF | Relativistic Self-consistent Field |
| RSCPA | Reduced (second Order) Self-consistent Phonon Approxn. (a Green-function Calcn. Method) |