- OASE, National University of Tainan, Taiwan
- Observatoire aquitain des sciences de l'univers
- Observatoire astronomique de Strasbourg
- OCAD
- OCAD University
- OcalmPro
- Office Européen des Brevets
- ONERA - The French Aerospace Lab [Châtillon]
- ONERA - The French Aerospace Lab [Lille]
- ONERA - The French Aerospace Lab [Meudon]
- ONERA - The French Aerospace Lab [Palaiseau]
- ONERA - The French Aerospace Lab [Toulouse]
- ONERA, Université Paris Saclay [Palaiseau]
- Ontario Institute for Cancer Research [Canada]
- Ontario Research Center for Computer Algebra
- Open Knowledge Foundation
- OpenTrust
- Operational Research and Optimization
- Optimisation, Simulation, Risque et Statistiques pour les Marchés de l’Energie
- Optimisation thérapeutique en Neuropsychopharmacologie
- Orange Labs [Belfort]
- Orange Labs [Caen]
- Orange Labs [Cesson-Sévigné]
- Orange Labs [Chatillon]
- Orange Labs [Issy les Moulineaux]
- Orange Labs [Lannion]
- Orange Labs [Paris]
- Orange Labs R&D [Rennes]
- ORCCA and Computer Science Department
- Orell Füssli
- Oxford Centre for Functional Magnetic Resonance Imaging of the Brain
- Oxford e-Research Centre [Oxford]
- Oxford Internet Institute
- Oxford University Computing Services