OPA
- Ambae Island
- Anglican Order of Preachers
- Cloud Native Computing Foundation
- Dorus Rijkers
- FC OPA
- Fantasy Zone
- First Ivorian Civil War
- Hopa (disambiguation)
- Leviathan Wakes
- List of gravitational wave observations
- Maricopa people
- Matthew Modine
- OPA Co., Ltd.
- OPA mixture
- Obscene Publications Act 1959
- Office of Population Affairs
- Office of Price Administration
- Office of the Pardon Attorney
- Oil Pollution Act of 1990
- Oil and Pipelines Agency
- Oligo Pool Assay
- Omega Phi Alpha
- Omni-Path
- Online Privacy Alliance
- Ontario Power Authority
- Opa (Swedish band)
- Opa (Uruguayan band)
- Opa (expression)
- Opa (programming language)
- Opa (roller coaster)
- Opa (song)
- Opa Muchinguri
- Opa Nguette
- Opa Opa
- Opa Opa (album)
- Opa Station
- Open Platform Architecture
- Optical parametric amplifier
- Optical phased array
- Oracle Policy Automation
- Ordre des Palmes Academiques
- Oregon Pioneer Association
- Oregon Potters Association
- Oropharyngeal airway
- Ortho-phthalaldehyde
- Out-patient
- Outward Processing Arrangement
- Ovine pulmonary adenocarcinoma
- Scandal (American TV series)
- Tea leaf grading
- The Expanse (TV series)
- Toyota Opa
- U.S. Office of Palestinian Affairs