- CAD Computer-Aided Design
- CADD Computer-Aided Design and Drafting
- CADE Computer-Aided Document Engineering
- CAE Computer-Aided Engineering
- CAI Computer-Aided Instruction
- CALS Computer-aided Acquisition and Logistic Support / Continuous Acquisition and Lifecycle Support
- CAM Computer-Aided Manufacturing / Common Access Method
- CAN Campus Area Network
- CARL Colorado Alliance of Research Libraries
- CAS Communications Application Specification
- CASE Computer-Aided Systems Engineering / Computer-Aided Software Engineering
- CAT Computer Adaptive Testing
- CATV CAble TeleVision
- CAVE Cave Automatic Virtual Environment
- CB Create Button / Citizen's Band
- CBB Change Button Binding
- CBE Computer-Based Education
- CBET Computer Based Education and Training
- CBIOS Compatibility BIOS
- CBM Commodore Business Machines
- CBT Computer-Based Training
- CCD Charge-Coupled Device / Charge-Coupled Diode
- CCIRN Coordinating Committee for Intercontinental Research Networks
- CCIS Common Channel Interoffice Signaling
- CCITT Comite Consultatif International de Telegraphique et Telephonique
- CCL Connection Control Language
- CCR Commitment, Concurrency and Recovery
- CCS Common Command Set
- CD Compact Disk / Change Directory / Carrier Detect
- CD-I Compact Disk Interactive
- CD-R Compact Disk Recordable
- CD-ROM Compact Disk Read Only Memory
- CDE Common Desktop Environment
- Cdev Control Panel DEVice
- CDK Control Development Kit
- CDMA Code Division Multiple Access
- CDPU Cellular Digital Packet Data
- CDR Constant Density Recording
- CERT Computer Emergency Response Team
- CES Consumer Electronics Show
- CFR Computerized Facial Recognition
- CFV Call For Votes
- CGA Color Graphics Adapter
- CGI Common Gateway Interface
- CGM Computer Graphics Metafile
- CI Check Item
- CIB Change Item Binding
- CICS Customer Information Communication System
- CIE Commercial Internet Exchange / Commission Internationale de l'Eclairage
- CIM CompuServe Information Manager
- CIS Card Information Structure / Compuserve Information Service
- CISC Complex Instruction Set Computer
- CIX Commercial Internet EXchange
- CLASS Custom Local-Area Signaling Services
- CLC Color Laser Copier
- CLI Call-Level Interface
- CLNS ConnectionLess Network Services / ConnectionLess-mode Network Services
- CLTP ConnectionLess Transport Protocol
- CMC Common Messaging Calls
- CMIP Common Management Information Protocol
- CMIS Common Management Information Services
- CMOL CMIP On IEEE 802.2 Logical Link Control
- CMOS Complementary Metal Oxide Semiconductor
- CMOT Common Management Information Protocol Over TCP/IP
- CMS Conversational Monitor System
- CMY Cyan Magenta Yellow
- CMYK Cyan Magenta Yellow BlacK
- CNI Coalition for Networked Information
- CNIDR Clearinghouse for Networked Information Discovery and Retrieval
- COBOL COmmon Business Oriented Language
- CODE Client/server Open Development Environment
- CODEC COmpression DECompression
- COM Common Object Model
- CONS COnnection-mode Network Services
- CORBA Common Object Request Broker Architecture
- COS Corporation for Open Systems
- CoSN Consortium for School Networking
- CP/M Control Program for Microcomputers
- CPE Customer Premises Equipment / Convergence Protocol Entity
- CPN Compuserve Packet Network
- CPR Computerized Patient Records
- CPS Cycles Per Second
- CPU Central Processing Unit
- CRC Cyclic Redundancy Check / Computer Records Center
- CREN Corporation for Research and Networking
- CRS Configuration Report Server
- CRT Cathode Ray Tube
- CS Clear to Send
- CSD Computer Services Organization
- CSLIP Compressed Serial Line Internet Protocol
- CSMA/CD Carrier-Sense Multiple-Access/Collision-Detect(ion)
- CSNET Computer+Science NETwork
- CSU Channel Service Unit
- CSU/DSU Channel Service Unit/Data Service Unit / Channel Service Unit/Digital Service Unit
- CSV Comma-Separated Values
- CTB Communications ToolBox
- CTERM Communications TERMinal Protocol / Command TERMinal Protocol
- CTI Computer/Telephony Interconnect
- CTS Carpal Tunnel Syndrome / Clear To Send
- CUA Common User Access
- CUI Common User Interface
- CWIS Campus Wide Information System