C9

C9, C09 or C-9 may refer to:

==Biology, medicine, and chemistry== C9 (Complement component 9), a protein ATC code C09, a subgroup of the Anatomical Therapeutic Chemical Classification System C09, ICD-10 code for malignant neoplasm of tonsil Carbon-9 (C-9 or 9C), an isotope of carbon Coccinella novemnotata, the nine-spotted ladybug or C9, a species of lady beetle