O
- Obernai
- Pully, Switzerland
- Offranville
- Thurmaston, England, UK
- Oignies
- Mutterstadt, Germany
- Ollainville
- Tutbury, England, UK
- Omerville
- Llangedwyn, Wales, UK
- Orchies
- Kelso, Scotland, UK
- Ormesson-sur-Marne
- Northallerton, England, UK
- Orange
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- Orgerus
- Washingborough, England, UK
- Orléans
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- Orly
- Klin, Russia
- Campi Bisenzio, Italy
- Turnu Severin, Romania
- Ornans
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- Orphin
- Charmey, Switzerland
- Orvault
- Târgovişte, Romania
- Ouistreham-Riva Bella
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- Oullins
- Nürtingen, Germany
- Ouzouer-sur-Loire
- Great Ayton, England, UK
Read more about this topic: List Of Twin Towns And Sister Cities In France