- Oak Crest Institute of Science
- Oak Ridge Leadership Computing Facility
- Oak Ridge National Laboratory
- Oak Ridge National Laboratory - US ITER
- Oakland University
- Oberlin College
- Obesity Society
- Ocean Networks Canada
- Office of Naval Research
- Ohio State University Medical Center
- Ohio Supercomputer Center
- Ohio University
- Okayama University
- Okinawa Institute of Science and Technology
- Optica
- Oregon Health & Science University
- Oregon Research Institute
- Oregon State University
- Orlando Health
- Osaka City University
- Osaka Metropolitan University
- Osaka University
- Ottawa Hospital Research Institute
- Oxford Brookes University
- Oxford Martin School
- Oxford University Press
