GSI may refer to:
- Several geographical or geological organisations:
- Geological Survey of India
- Geological Survey of Iran
- Geographical Society of Ireland
- Geological Survey of Ireland
- Geological Survey of Israel
- Geographical Survey Institute of Japan
- Gemological Science International, a gemstone assessment laboratory
- Geological Strength Index
- Geophysical Service Incorporated, a petroleum exploration corporation
- Gesellschaft für Schwerionenforschung, a German heavy ion research laboratory in Darmstadt, Hesse
- GSI Commerce, a shopping website design company
- GSI Outdoors, an outdoors cookware company
- Grid Security Infrastructure, a specification for tamperproof computer networks
- Government Secure Intranet, the system for managing secure access to e-mail and other services for UK government departments
- Good Shepherd Institute
- Guangzhou Shipyard International, a shipbuilding state-owned enterprise in the People's Republic of China
- Graduate Student Instructor, or teaching assistant
- Gonadosomatic Index
- Global System Interrupt in Advanced Configuration and Power Interface for Intel APIC Architecture.
- Gridpoint Statistical Interpolation, a type of data assimilation.