CSI
- CSI (comics)
- CSI (franchise)
- CSI (novels)
- CSI (video games)
- CSI 300 Index
- CSI Sanatan
- California Solar Initiative
- Camera Serial Interface
- Canadian Securities Institute
- Carnaby Street (radio programme)
- Centre for Social Impact
- Centre for Social Innovation
- Centre for Social Investigation
- Channel state information
- Chlorosulfonyl isocyanate
- Christian Schools International
- Christian Solidarity International
- Church of Scientology International
- Church of South India
- City Supermarket, Inc.
- Cité Scolaire Internationale de Grenoble
- Cité Scolaire Internationale de Lyon
- Cité des Sciences et de l'Industrie
- Civilian Saucer Intelligence
- Coherence scanning interferometry
- College of Southern Idaho
- College of Staten Island
- Commission Sportive Internationale
- Committee for Skeptical Inquiry
- Common System Interface
- Companion of the Order of the Star of India
- Complex specified information
- Computer Security Institute
- Computer Society of India
- Computers and Structures, Inc.
- Concours de Saut International
- Conditional symmetric instability
- Consorzio Suonatori Indipendenti
- Construction Specifications Institute
- Container Security Initiative
- Control Sequence Introducer
- Crime Stoppers International
- Crime scene investigation (disambiguation)
- Cross of Solomon Islands
- Crystalline silicon
- CueSports International
- Customer satisfaction
- Railway Safety Commission