CIS
- ACT-CIS Partylist
- Bosch K-Jetronic
- CIS Corps (Ireland)
- CIS Tower
- CIS national football team
- Calcutta International School
- Canadian Ice Service
- Canadian Identification Society
- Canadian International School (Bangalore)
- Canadian International School (Singapore)
- Canadian International School (Tokyo)
- Canadian International School (disambiguation)
- Canadian International School Vietnam
- Canadian International School of Sanya
- Canadian Interuniversity Sport
- Cancer Information Service
- Canton Island Airport
- Capital Indoor Stadium
- Carcinoma in situ
- Card information structure
- Case Information Statement
- Cayman International School
- Cebu International School
- Center for Immigration Studies
- Center for Internet Security
- Center for Internet and Society (disambiguation)
- Centre for Independent Studies
- Centro de Investigaciones Sociológicas
- Chinese International School
- Christians in Science
- Cis (disambiguation)
- Cisalpino
- Clifford International School
- Clinically isolated syndrome
- Co-operative Insurance Society
- College in the Schools
- Colombo International School
- Combined intracavernous injection and stimulation test
- Common Intelligibility Scale
- Commonwealth Police
- Commonwealth of Independent States
- Communities In Schools
- Community Innovation Survey
- Comodo Internet Security
- CompuServe Information Service
- Computer and information science
- Computer information system
- Confederacy of Independent Systems
- Configuration interaction singles
- Contact image sensor
- Continuous ink system
- Copenhagen International School
- Copper indium selenide
- Corpus Inscriptionum Semiticarum
- Council of International Schools
- MIT Center for International Studies
- United States Citizenship and Immigration Services