- O'Donovan Consulting AG
- OBO Bettermann Holding GmbH & Co. KG
- ODS-Office Data Service GmbH
- Oest Holding GmbH
- Oetker Collection
- Oikos Group GmbH
- Oliver Schrott Kommunikation GmbH
- Optibus Ltd
- OPTIMA packaging group GmbH
- OQEMA AG
- oraise GmbH
- Organization for Science, Education and Global Society gGmbH
- Orizon Holding GmbH
- ORYX GmbH
- OTTO KRAHN (GmbH & Co.) KG
- Ottobock SE & Co. KGaA