Ob may refer to:
- Ob River, a river in West Siberia, Russia
- Ob Sea, an artificial lake on the Ob River
- Ob, Russia, a town in Novosibirsk Oblast, Russia
- Ob, Germany, place in Bidingen, Bavaria, Germany
- Gulf of Ob, a bay of the Arctic Ocean in Northern Russia
- Object Manager (Windows), a Windows NT subsystem
- The fictional currency of the Gands in Eric Frank Russell's The Great Explosion