CSI may refer to:

• CSI (franchise)
  • CSI: Crime Scene Investigation, the original CSI television series, set in Las Vegas
  • CSI: Miami, the first spin-off series starring David Caruso
  • CSI: NY, the second spin-off series starring Gary Sinise
  • CSI: Cyber, the third spin-off series starring Patricia Arquette
  • CSI: Vegas, the fourth spin-off series and a sequel to the original
  • CSI: Trilogy, the three-part television event featuring the casts of CSI: Crime Scene Investigation, CSI: Miami, and CSI: NY
  • CSI (comics)
  • CSI (novels)
  • CSI (video games)
  • CSI: The Experience, a traveling exhibition

• Consorzio Suonatori Indipendenti, an Italian musical group
• CSI:Ambleside, a 2008 album by British band Half Man Half Biscuit

• CSI Sanatan, 2023 Indian Telugu-language film by Sivashankar Dev
• Carnaby Street (radio programme), Saturday morning Manx Radio broadcast featuring music and news from the 1960s

• Centre for Social Impact, a network of research centres across four Australian universities
• Centre for Social Innovation, a social enterprise based in Toronto, Canada
• Centre for Social Investigation, an interdisciplinary research group in Oxford, England
• City Supermarket, Inc., a grocery chain based in Pangasinan, Philippines
• Coimisiún Sábháilteachta Iarnróid, the Railway Safety Commission of Ireland
• Computer Security Institute, a former professional association in the United States
• Computer Society of India, a professional association
• Computers and Structures, Inc., a structural engineering software company
• Construction Specifications Institute, a technical society in the United States
• Crime Stoppers International

• Civilian Saucer Intelligence, an unidentified flying object research group
• Committee for Skeptical Inquiry, an organization for skeptical paranormal investigation

• Cité des Sciences et de l'Industrie in Paris

• Companion of the Order of the Star of India, a class of the order of chivalry founded by Queen Victoria
• Cross of Solomon Islands, a class of the Order of the Solomon Islands

• Christian Schools International
• Christian Solidarity International
• Church of Scientology International
• Church of South India

• Canadian Securities Institute, a financial education company providing professional credentials and compliance courses
• Cité Scolaire Internationale de Grenoble, an international school in Grenoble, France
• Cité Scolaire Internationale de Lyon, an international school in Lyon, France
• College of Southern Idaho, a community college in the United States
• College of Staten Island, part of The City University of New York in the United States

• Commission Sportive Internationale, a governing body for motor racing
• Concours de Saut International, a ranking system for show jumping
• CueSports International, a pool (pocket billiards) event promotion company and league organizer, affiliated with the Billiard Congress of America

• Camera Serial Interface, an MIPI Alliance protocol for cameras and mobile devices
• Channel state information, a wireless communication term
• Coherence scanning interferometry, an areal surface topography technique related to 3D interference microscopy
• Common System Interface, a former name of the Intel QuickPath Interconnect, a computer bus
• Control Sequence Introducer, a control character for initiating escape sequences
• Crystalline silicon (c-Si), used in solar cell technology
• Conditional symmetric instability, a form of convective instability in a fluid

• California Solar Initiative, a renewable energy program
• Chlorosulfonyl isocyanate
• Complex specified information, an argument for intelligent design
• Container Security Initiative, a program of the U.S. Bureau of Customs and Border Protection
• CSI 300 Index, a stock market index compiled by the China Securities Index Company
• Customer satisfaction index, a metric that reflects the overall customer satisfaction with a company in terms of product quality, customer service, price, etc.

• Crime scene investigation (disambiguation)