CO

CO or variants may refer to:

Chemistry

.co (second-level domain), the Internet second-level domain meaning "commercial"
.co, the Internet country code top-level domain (ccTLD) for Colombia
Commitment ordering (CO), a concurrency control technique for databases
Telephone exchange, or central office (CO)

C.O., post-nominal initials of members of the congregation of the Oratory of Saint Philip Neri
C/O, cadet officer ranks of the Junior Reserve Officers' Training Corps
Commanding officer (CO), the officer in command of a military unit
Contracting Officer (CO or KO), in the U.S. government
Correctional officer (CO), an officer whose duty it is to safeguard and promote the welfare of inmates
Circle officer (CO), in the Indian government
Conscientious objector

Chemins de fer Orientaux (CO), a former Ottoman railway company
Chesapeake and Ohio Railway (C&O or CO), a former American railroad
Cobalt Air (IATA airline designator CO, 2016-2018), a Cypriot airline
Continental Airlines (IATA airline designator CO, 1937-2012), an American airline

In Italy, c/o, is an abbreviation used in postal shipments to indicate a person other than the recipient, but to whom the message is physically addressed.

co-, an English prefix meaning coming together
Cardiac output (CO), the volume of blood being pumped by the heart per time unit
Castres Olympique, a French rugby club
Certificate of occupancy (CO), a legal document
Certificate of origin (often abbreviated to C/O or CoO), in international trade
Company, abbreviated co.
Corsican language, ISO 639-1 language code co
c/o, a Unicode character in the Letterlike Symbols block
c/o, former name of Gerhardsen Gerner, an art gallery in Berlin