OPG may refer to:
- Osteoprotegerin
- Ocean Physics Group - OPG - Department of Marine Science, University of Otago, New Zealand
- ox Programming Group
- Object Process Graph
- Office of the Public Guardian
- Office of HM Paymaster General
- Oldroyd Publishing Group
- Online Policy Group
- Ontario Power Generation
- Optical parametric generator
- Orthopantomogram radiograph (a panoramic dental xray)
- Oriented pyrolytic graphite
- Outer product of gradient
- Original Parts Group