Otto-Suhr-Institut , the political-science institute of the Free University of Berlin
Option symbol#See also|Options Symbology Initiative , a plan to change the way that exchange-traded options are named
Open Systems International , an automation software vendor for the electric, petroleum, transportation and water industries
Open Systems Interconnection , ISO 7498, International Organization for Standardization
Osijek Airport , an airport in Croatia
Government
Office of Scientific Intelligence , former name of a department of the Central Intelligence Agency now called the Directorate of Science and Technology
Office of Strategic Influence , a short-lived former American government agency created in 2001, part of the Department of Defense and focused on psychological warfare
Office of Special Investigations, a name shared by several government agencies
* U.S. Air Force Office of Special Investigations
* Office of Special Investigations (Government Accountability Office)
* Office of Special Investigations (United States Department of Justice)
Office of Scientific Integrity, now United States Office of Research Integrity
Office of Special Investigation (Republic of Korea), a secret intelligence unit of Republic of Korea Air Force
Finance
OSI, acronym for Official Sector Involvement in sovereign debt restructuring deals, as opposed to Private sector involvement|PSI (Private Sector Involvement) .
Technology
Open Systems Interconnection , a joint ISO and ITU-T standard for computer networks and communication protocols
* OSI model , a layered description for communications and computer network protocol design
Open Source Initiative , an organization dedicated to promoting open source software
Ohio Scientific Inc., a microcomputer manufacturer from the late 1970s to the early 1980s
Open Switching Interval, a type of disconnect supervision
On-Site Inspection , an advanced measure technique combining several methods - especially used in order to detect nuclear tests
Officine Stampaggi Industriali , Italian coachbuilder
Entertainment
OSI (band) , an American progressive rock supergroup named after the former Office of Strategic Influence government agency
Origin Systems , a former United States computer game developer
Office of Strategic Influence (album)| Office of Strategic Influence (album) , the 2003 debut album by the band OSI
Fiction
" Office of Scientific Intelligence#Pop culture|Office of Scientific Intelligence ", a fictional United States government agency in several television programs and movies
" Office of Secret Intelligence ", a fictional United States government secret agency in the animated series The Venture Bros.
People
Osi Umenyiora , defensive end for the New York Giants
