IOA
- IEC 60870-5-104
- Independent Olympic Athletes
- Indian Olympic Association
- Input-output analysis
- Input/output
- Institute of Acoustics (United Kingdom)
- Institute of Acoustics, Chinese Academy of Sciences
- Institute of Astronomy, Cambridge
- International Olympic Academy
- International Ombudsman Association
- International Oversight Advisory
- Ioannina National Airport
- Irish Orienteering Association
- Islands of Adventure
- Orlando, Florida
- UCL Institute of Archaeology