GCI
- First Geneva Convention
- GCI (company)
- GCI coach
- Galt Collegiate Institute
- Gannett Company
- Gaussian correlation inequality
- Generalized conversational implicature
- Geomagnetically induced current
- Getty Conservation Institute
- Glass Ceiling Index
- Glebe Collegiate Institute
- Glen Canyon Institute
- Global Change Institute
- Global Cinematography Institute
- Global Competitiveness Index
- Google Code-in
- Government College Ikorodu
- Grace Communion International
- Grassroots Campaigns, Inc.
- Grating-coupled interferometry
- Great Coasters International
- Great Commission International
- Green Campus Initiative (UCT)
- Green Cross International
- Ground-controlled interception
- Guernsey Airport
- International Conference on the Situation in Venezuela