OSI is an abbreviation for a number of terms:

1. The Office of Strategic Influence was an United States government agency in the early 2000s.
2. OSI is a progressive rock band formed by members of Dream Theater and Fates Warning.
3. Office of Strategic Influence is the 2003 debut album by the band (OSI).
4. Ontario Swine Improvement is a pig breeding company based in Ontario, Canada.
5. Open Systems Interconnect is a joint ISO and ITU-T standard for computer networks and protocols.
6. Open Source Initiative is an organization dedicated to promoting open source software.
7. The Open Society Institute is a private foundation established by George Soros to promote open societies around the world.
8. The OSI model is a layered abstract description for communications and computer network protocol design
9. Ordnance Survey Ireland (Suirbhéireacht Ordanáis Éireann)
10. Origin Systems, Inc. is a computer game developer
11. The Office of Special Investigations is a name which has been used by several organizations:
    1. The U.S. DOJ Office of Special Investigations detects and investigates individuals in the United States who took part in Nazi-sponsored acts of persecution abroad before and during World War II.
    2. The U.S. Air Force Office of Special Investigations
    3. The U.S. GAO Office of Special Investigations
12. The Office of Scientific Intelligence was the name of a department of the Central Intelligence Agency now called the Directorate of Science and Technology .