| Current Issues in Sport Science | Academic & Science |
| Cast In Site Slab | Academic & Science |
| Counselor Initiative and Student Support | Academic & Science |
| Characteristics Instrument for Screening Students | Academic & Science |
| Internationaler Rat für Sozialwissenschaften | Academic & Science |
| Conseil International des Sciences Sociales | Academic & Science |
| Consejo Internacional de Ciencias Sociales | Academic & Science |
| International Social Science Council | Academic & Science |
| Computer Information Systems Society | Business |
| Certified information Security Specialist | Business |
| Conversational Intelligence Summer School | Community |
| Community Information Sharing System | Community |
| Conference on Information Sciences and Systems | Community |
| Conference on Information Systems and Sciences | Community |
| Computer Info Sci Security | Computing |
| Continuous Ink Supply System | Computing |
| Common Internet Scheme Syntax | Computing |
| Confirmation Interactive Site Server | Computing |
| Computerized Inventory System Specialists | Computing |
| Computer and Information Systems Security | Computing |
| Computer Information Systems Security | Computing |
| Composite Indicator Of Systemic Stress | General |
| Channel Islands Social Services | General |
| Computed Images System & Services | General |
| Connected Industrial Sensor Solution | General |
| Customer Information Support Specialist | General |
| Convergence Insufficiency Symptoms Survey | General |
| Convergence Insufficiency Symptom Survey | General |
| Chiral Induced Spin Selectivity | General |
| Cambridge International Scholarship Scheme | General |
| Centre for International Security Studies | General |
| Campbell Interest and Skill Survey | General |
| Comparative Interdisciplinary Studies Section | General |
| Critical Incident Support Services | General |
| Collaboration Inspiration Support and Swiftness | General |
| Crash Impact Sound Sensor | General |
| Cooperative Integrated Safety Systems | General |
| Center for Intelligence and Security Studies | General |
| Citizen Initiated State Statute | General |
| Comprehensive Import Supervision Scheme | General |
| Configurable Integrated Surveillance System | General |
| Connecticut Information Sharing System | General |
| Constructive Interference Steady State | General |
| Continuous Ink Supply Systems | General |
| Constructive Interference In Steady State | General |
| Comprehensive Information Security Switzerland | General |
| Consumer Injury Surveillance System | General |
| Crash Investigation Sampling System | Governmental |
| Center for Information Systems Security | Governmental |
| Community Integrated Service System | Governmental |
| Centaur Integrated Support Structure | Governmental |
| Concordia International School Shanghai | International |
| Comité International des Sports des Sourds | International |
| Center for International Students and Scholars | International |
| China International Student Service | International |
| China International Student System | International |
| Cancer Information and Support Services | Medical |
| Canadian International School System | Regional |
| Canadian ISBN Service System | Regional |
| Canadian International Student Services | Regional |
| Canadian Internetworked Scientific Supercomputer | Regional |
| Centre for International Sports Studies | Sports |