OPI may refer to:
- OPI Products, a nail beauty product brand
- Oremus Pro Invicem from the Latin, Let us Pray for each other (see List of Latin phrases (O))
- Open Payment Initiative
- Open Prepress Interface uses a network server to store images in order to reduce memory required for high-resolution document image layout.
- Over the phone interpreting
- Oral Proficiency Interview
- OPI (organisation) Order of Perpetual Indulgence (see Sisters of Perpetual Indulgence)
- Opi, Abruzzo, a comune in Italy
- C. opilio, a species of Chionoecetes crab
- Opi (instrument), an Igbo musical instrument
- The Office of Police Integrity, an independent agency formed by the Victorian Government investigating police corruption
- Online Provisioning Interface (Telecommunications: Intelligent Network element)
- Oklahoma Policy Institute