| Acronym | Meaning |
| CAROL | Centralized Air Emissions Repository On-Line |
| CARPT | Computer Automated Radioactive Particle Tracking |
| CARRI | Computerized Assessment Of Relative Risk Impacts |
| CARS | Corrective Action Reporting System (now Known As RCRIS) |
| CARS | Coherent Anti-Stokes Raman Spectroscopy |
| CART | Classification And Regression Tree (method In Statistical Analysis) |
| CART | Cloud And Radiation Testbed |
| CART | Cocaine And Amphetamine Regulated Transcript |
| CARTS | Critical Actions Requirements Tracking System |
| CAS | Chemical Abstracts Service |
| CAS-CI | Complete Active Space-configuration Interaction |
| CAS-MC-SCF | Complete Active Space-multiconfiguration-SCF |
| CAS-SCF | Complete Active Space SCF (a CI-type Method) |
| CAS-SI | Complete Active Space-state Interaction |
| CASAC | Clean Air Scientific Advisory Committee (US EPA) |
| CASARM | Chemical Agent Standard Analytical Reference Material |
| CASE | Computer Assisted Structure Elucidation |
| CASE | Coordinated Air Sea Experiment |
| CASE | Computer Aided Software Engineering |
| CASH | CaO-Al2O3-SiO2-H2O System |
| CASI | Compact Airborne Spectrographic Imager |
| CASP | Computer-assisted Synthesis Planning |
| CASPT | Complete Active Space-perturbation Theory |
| CASPT2 | Complete Active Space With Second-order Perturbation Theory |
| CASR | Chemical Activity Status Report |
| CASRN | Chemical Abstracts Service Registry Number |
| CASS | Computer Assisted Stratification And Sampling |
| CASS | Cyclic Activated Sludge System |
| CASSCF | Complete Active Space-self Consistent Field |
| CASSCF-CCI | Complete Active Space Self-consistent Field-contracted CI |
| CASSS | California Separation Science Society |
| CAST | CERN Axion Solar Telescope |
| CAST | Council For Agricultural Science And Technology |
| CAST | Cyclic Activated Sludge Technol. |
| CASTNET | Clean Air Status And Trends Network |
| CASV-MC-SCF | Complete Active Space Valence Space-multiconfiguration-SCF |
| CAT | Chloramphenicol Acetyltransferase |
| CAT | Clear Air Turbulence |
| CAT | Computer-aided Tomography |
| CATA | Computer-aided Thermal Anal. |
| CATC | Cyanide Amenable To Chlorination |
| CATS | Corrective Action Tracking System |
| CATSAT | Cooperative Astrophysics And Technology Satellite |
| CATSI | Compact Atmospheric Sounding Interferometer |
| CAU | Carbon Adsorption Unit |
| CAUGA | Clifford Algebra Unitary Group Approach |
| CAW | Carbon Arc Welding |
| CAWAI | Commission On Atomic Weights And Isotope Abundances |
| CAWC | Cryogenic Aerosol Wafer Cleaning |
| CAWG | Clean Air Working Group |