| Acronym | Definition |
|---|
| OPA | Office of Public Affairs |
| OPA | Ontario Power Authority (Ontario, Canada) |
| OPA | Online Publishers Association |
| OPA | Oil Pollution Act of 1990 |
| OPA | Oil Painters of America |
| OPA | Offre Publique d'Achat |
| OPA | Oferta Pública de Adquisición (de Acciones) |
| OPA | Oferta Publica de Adquisicion (Spanish) |
| OPA | Online Payment Agreement (taxes) |
| OPA | Otherwise Protected Area |
| OPA | Opacity-Associated |
| OPA | Office of the Provincial Agriculturist (Philippines) |
| OPA | Online Pool Analyzer |
| OPA | Optical Pre Amplifier |
| OPA | Online Public Access |
| OPA | Office of Price Administration |
| OPA | Offerta Pubblica Di Acquisto (Italian) |
| OPA | Office of Population Affairs |
| OPA | Opsonophagocytic Assay (microbiology) |
| OPA | Office of Protection and Advocacy (aka P&A; persons with disabilities; Connecticut) |
| OPA | Office of the Patient Advocate |
| OPA | Official Points of Acceptance (investing) |
| OPA | Office of Public Advocacy (various locations) |
| OPA | Office of Professional Accountability (Seattle Police Department) |
| OPA | Oropharyngeal Airway |
| OPA | Ontario Pharmacists' Association |
| OPA | Office of Pharmacy Affairs (HHS) |
| OPA | Optical Parametric Amplifier |
| OPA | Online Privacy Alliance |
| OPA | Open Patent Alliance |
| OPA | Oklahoma Press Association |
| OPA | Open Partial Agreement (EU) |
| OPA | Outward Processing Arrangement (Hong Kong and China) |
| OPA | Ohio Pharmacists Association |
| OPA | Optic Atrophy |
| OPA | Ontario Psychological Association |
| OPA | Overseas Publishers Association |
| OPA | Office of Payroll Administration |
| OPA | Opera Primaziale Pisana (Italian social accountability policy) |
| OPA | Ontario Parks Association (Canada) |
| OPA | Office of Policy Analysis |
| OPA | Other Procurement, Army |
| OPA | Official Public Account (Australia) |
| OPA | Office of Public Assistance |
| OPA | Office of Planning and Analysis (various locations) |
| OPA | Oregon Paralegal Association |
| OPA | Ontario Prospectors Association |
| OPA | Ontario Paramedic Association |
| OPA | Office of Program Appraisal |
| OPA | Offshore Petroleum Act 2006 (Australia) |
| OPA | Oriented Polyamide |
| OPA | Operations, Army |
| OPA | Office of Premarket Approval |
| OPA | Okinawa Prefectural Archives (est. 1995; Japan) |
| OPA | Ortho-Phthaldialdehyde |
| OPA | Optical Publishing Association |
| OPA | Observations Programme Area (JCOMM) |
| OPA | Other Principal Arterial (transportation) |
| OPA | Outstanding Paper Award |
| OPA | Offenporigen Asphaltdeckschicht (German: Porous Asphalt Surface Layer) |
| OPA | Organization of Professional Aviculturists |
| OPA | Offense Per Acre (gaming) |
| OPA | Organization for Public Administration |
| OPA | Orthopedic Professional Association (Gilford, New Hampshire) |
| OPA | Ohio Poetry Association (Ohio) |
| OPA | Officer Personnel Act |
| OPA | Open Platform Architecture |
| OPA | Organization of Professional Associations of Sri Lanka |
| OPA | Office of Professional Attachment |
| OPA | Out of Place Artifact |
| OPA | Orthopaedic Practice Assembly (Medical Group Management Association) |
| OPA | Overarching Partnering Agreement |
| OPA | Ontario Physiotherapists Association |
| OPA | Ouptut and Performance Analysis |
| OPA | OSI Presentation Address |
| OPA | Operations Procurement Authority |
| OPA | Other Procurement Authority |
| OPA | Open Planar Array |
| OPA | Overhead Precautionary Approach |
| OPA | Organizational Performance Architecture |
| OPA | Operator Panel Assembly |
| OPA | Outage Probability Analysis |