| OPI | Objectif Projet Individuel | In French | |
| OPI | Operations Procedure Instruction | In English | → Management |
| OPI | Orbiter Payload Interrogator | In English | → Spaceflight engineering, astronautics |
| OPI | Ośrodek Przetwarzania Informacji (www.opi.org.pl) | In Polish | → Research policy |
| OPI | Office du Périmètre d'Irrigation | In French | → Public administration, government → Agricultural sciences |
|