OCI
- Internationalist Communist Organisation
- Lisgar Collegiate Institute
- OCI (company)
- Oakwood Collegiate Institute
- Occitan language
- Office of Criminal Investigations
- Olympic Council of Ireland
- Ontario Cancer Institute
- Open Catalog Interface
- Open Constitution Initiative
- Open Container Initiative
- Oracle Call Interface
- Orascom Construction
- Order of the Crown of Italy
- Organizational conflict of interest
- Other comprehensive income
- Overseas Citizen of India