| CAST | Chinese Academy of Space Technology (CN) |
| CB | Citizen Band |
| CCIR | Comité Consultatif International des Radiocommunications (ITU) |
| CCITT | Comité Consultatif International de Télégraph et des Télécommunications (ITU) |
| CCMS | Committee on Challenges of Modern Science (NATO) |
| CCSDS | Consultative Committee on Space Data Systems |
| CDMA | Code Division Multiple Access |
| CE | Conformité Européenne (label for conformity to European Directives) |
| CENELEC | European Committee for Electrotechnical Standardization |
| CEPT | Conférence Européene des Postes et des Télécommunications |
| CERGA | Centre d’Etudes et de Recherches Géodynamiques et Astronomiques |
| CGMS | Coordination on Geostationary Meteorological Satellites |
| C/I | Carrier-to-intermodulation products |
| CICG | Centre International des Conférences Genève |
| CIE | Commission Internationale d’Eclairage |
| CIMO | Commission on Instruments and Methods of Observations (WMO) |
| CIRM | Committee International Radio Maritime |
| CISPR | International Special Commitee on Radio Interference |
| CITEL | Inter-American Conference on Telecommunications |
| (Conferencia Interamericana de Telecommunicaciones) | |
| CMTT | Joint Study Group for Television and Sound Transmission |
| CNES | Centre National d’Etudes Spatiales (F) |
| CNET | Centre National d’Etudes des Télécommunications (F) |
| CNIE | Comision Nacional de Investigaciones Espaciales |
| CNR | Carrier-to-noise ratio |
| CNRS | Centre National de Recherches Scientifiques (F) |
| CODATA | Committee on Data for Science and Technology |
| COFDM | Coded Orthogonal Frequency Division Multiplex |
| COMSAT | Communications Satellite Corporation (USA) |
| COPUOS | UN Commission on the Peaceful Use of Outer Space |
| CORF | Commission on Radio Frequencies (NRC-USA) |
| COSPAR | Committee on Space Research |
| COSPAS | Russian system of Satellite Search and Rescue |
| COSTED | Committee on Science and Technology in Developing Countries |
| CPE | Customers premises equipment |
| CPEM | Conference on Precision Electromagnetic Measurements |
| CPG | Conference Preparatory Group (CEPT) |
| CPM | Conference Preparatory Meeting (ITU) |
| CRAF | Committee on Radio Astronomical Frequencies (ESF) |
| CSA | Canadian Space Agency (CDN) |
| CSIRO | Commonwealth Scientific and Industrial Research Organization |
| CSTG | Commission for International Coordination of Space Techniques for Geodesy and Geodynamics |
| CT | Cordless Telephone |
| CTO | Commonwealth Telecommunications Organisation |
| CTR | Common Technical Regulation (ETSI) |
| CW | Continuous Wave |