- Oakland University
- Oak Ridge National Laboratory [Oak Ridge]
- OAS AG
- Oberthur Technologies
- Objets communicants pour l'Internet du futur
- O Boticário
- Observatório do Valongo|UFRJ [Rio de Janeiro]
- Óbuda University [Budapest]
- Ocean College
- Oceaneering, Integrity Management & Digital Solutions
- Ocean House [Bracknell]
- Oceans and Atmosphere Flagship [Brisbane]
- Ocean University of China
- Ochanomizu University
- Œuvre de village d’enfants
- Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office
- OFFIS Institute for Information Technology
- Ohio University
- Oil Crops Research Institute
- Okayama University
- ØK Data [Copenhagen]
- Oklahoma State University [Stillwater]
- OKUMA Corporation
- OKYS [Sofia]
- Olayan School of Business
- Old Dominion University [Norfolk]
- Olympic Carillon
- OMiLAB
- OMP France
- Onaos [Montpellier]
- ONERA
- ONERA - The French Aerospace Lab [Toulouse]
- OneSource, Consultoria Informatica, Lda.
- OneSource, Consultoria Informática Lda. [Coimbra]
- Ontoprise GmbH [Karlsruhe]
- Opendawn
- OpenForum Europe
- Open Government Data Austria
- Open Invention Network
- OpenMRS
- Open Universiteit Nederland [Heerlen]
- Open University of Catalonia [Barcelona]
- Open University of Cyprus
- Open University of the Netherlands [Heerlen]
- Opole University of Technology
- Oracle
- Orange Communications SA
- Orange Labs
- Orange Labs [Caen]
- Orange Labs [Cesson-Sévigné]
- Orange Labs [Chatillon]
- Orange Labs [Issy les Moulineaux]
- Orange Labs [Lannion]
- Orange Labs SOP|BIZZ|DIAM
- Orange Labs [Sophia Antipolis]
- Orange Polska
- Örebro University
- Örebro University School of Business
- Oregon Health and Science University [Portland]
- Oregon State University
- Orenburg State University [Russia]
- Organisation Mondiale de la Santé | World Health Organization Office [Genève, Suisse]
- Organização Multinacional de Formação
- Orion Innovations P.C.
- Orkel AS
- Ortlinghaus-Werke GmbH
- Osaka City University Hospital
- Osaka Electro-Communication University
- Osaka Gakuin University
- Osaka International University
- Osaka Jikei Research Center of Healthcare Management
- Osaka Prefecture University
- Osaka University
- Osaka University hospital
- Osaka University of Economics
- Osaka University [Osaka]
- Osala Prefectuture University
- Oslo and Akershus University College of Applied Sciences [Oslo]
- Oslo Metropolitan University
- Oslo University Library
- Ostfalia University of Applied Sciences
- Østfold Hospital
- Oticon A|S [Danemark]
- Otto-von-Guericke-Universität Magdeburg = Otto-von-Guericke University [Magdeburg]
- Oulu University Hospital [Oulu]
- Oulu University of Applied Sciences
- Our Lady of the Lake University
- OvG University
- OW2 Consortium
- Oxfam GB
- Oxford Brookes University
- Oxford e-Research Centre [Oxford]
- Oxford-Man Institute of Quantitative Finance
- Oxford University Computing Laboratory
- OYO Hotels & Homes Pvt Ltd [Gurgaon]
- Özyeğin University