C9
- 9C (disambiguation)
- ATC code C09
- C-9 (Cercanías Madrid)
- C9 Entertainment
- C9 LMG
- C9 League
- Carbon-9
- Caterpillar Inc.
- Champion (sportswear)
- Cierva C.9
- Cirrus Airlines
- Cloud9 (esports organization)
- Complement component 9
- Council of Cardinal Advisers
- Ford C-9
- HMS C9
- Head and neck cancer
- ISO 216
- LNER Class C9
- Madrid
- McDonnell Douglas C-9
- Middle C
- Models C9 and C9 Comp
- Nachtjagdgeschwader 5
- SL C9
- Sauber C9
- USS Montgomery (C-9)