C2 or a derivative (C-2, C², etc.) may refer to:

Mathematics and physics

Biology

C2 domain, a protein structural domain
C2 regulatory sequence for the insulin gene
Apolipoprotein C2, a human apolipoprotein
In human anatomy, C2 may refer to:
- Cervical vertebra 2, the axis, one of the cervical vertebrae of the vertebral column
- Cervical spinal nerve 2
Chlorophyll c2, a form of chlorophyll
Complement component 2
Procyanidin C2, a plant phenolic compound
Prodelphinidin C2, a plant phenolic compound
Vitamin C2, a name sometimes used for Choline
the ATC code for Antihypertensives, a subgroup of the Anatomical Therapeutic Chemical Classification System
C₂ fragments, one of the types of products of catabolism pathways
Haplogroup C-M217, also known as C2, a Human Y-chromosome DNA haplogroup

C2 may be a code or abbreviation for:

C² Aquarii, a star
C² Centauri, a star
C2 (Code Geass), an anime character
C2 explosive, a form of plastic explosive
C2 pylon, a type of high voltage pylon
C2 (radio), a Welsh language music show on BBC Radio Cymru
C2 radio class, a class in FM broadcasting in America
C2 (classification), a para-cycling classification
Group C2, the secondary class of Group C sports car racing
BRDC C2 Championship, a short lived sports car racing series which ran from 1988 to 1990
Nimrod NRA/C2, a 1982 Group C racing car
C2, an international standard paper size defined in ISO 216 (458×648 mm)
C2, a level in the Common European Framework of Reference for Languages
C2, the NRS social grade between C1 and D
Command and control, the exercise of authority by a commanding officer over military forces in the accomplishment of a mission
Air Luxor IATA airline code
C2 Pictures, a film company related to Carolco Pictures
Bill C-2 from Canadian law, an act to amend the Criminal Code and the Canada Evidence Act
C2, or C₂ a note-octave in music, aka Low C

C2, a computer security class, defined in the Trusted Computer System Evaluation Criteria
C2, a bytecode compiler that is part of the HotSpot virtual machine implementation
C2 (protocol), a 1985 Commodore file transfer protocol
C2 error, a read error of a compact disc
C2.com or WikiWikiWeb, the first user-editable website
Cryptomeria cipher, a cipher used in digital rights management

C2 class Melbourne tram
Bavarian C II (Ostbahn), an 1862 German steam locomotive
Bavarian C II.1, an 1857 German steam locomotive
Bavarian C II.2, an 1861 German steam locomotive
Chevrolet Corvette (C2), the generation of the Chevrolet Corvette produced between 1962 and 1967
Citroën C2, a car produced by Citroën in 2004
Cluster II (spacecraft), an ESA space mission
GNR Class C2, a British 4-4-2 steam locomotive
Kawasaki C2, a bike
London Buses route C2
LB&SCR C2 class, an 1893 British 0-6-0 steam locomotive
Circumferential Road 2 or C-2, an arterial road of Manila, Philippines
Saf-T-Liner C2, a school bus built by Thomas Built Buses
Saturn C-2, a 1960 conceptual American launch vehicle
Type C2 ship, a type of all-purpose cargo ship
C2 (yacht), a luxury motor yacht
Central Circular Route (Shuto Expressway) in Tokyo, Japan
Nagoya-Daini-Kanjō Expressway, route C2 in Nagoya, Japan

C2A1, Squad Automatic Weapon variant of the FN FAL formerly in Canadian Service
C-2 Greyhound, the Grumman cargo aircraft of the United States Navy
ACAZ C.2, a Belgian prototype fighter aircraft of the 1920s
AEG C.II, a German World War II armed reconnaissance aircraft
AGO C.II, a German reconnaissance biplane of World War I
Cierva C.2, a 1921 Spanish experimental autogyro
DFW C.II, a World War I German reconnaissance aircraft
Fokker C-2, the American military version of the Fokker F.VII aircraft
HMS C2, a British C class submarine of the Royal Navy
Kawasaki C-2, a military transport aircraft
LFG Roland C.II, a 1915 advanced German reconnaissance aircraft
LVG C.II, a 1910s German two-seat reconnaissance biplane
USS C-2 (SS-13), a C-class submarine of the United States Navy
USS Charleston (C-2), a protected cruiser of the United States Navy
A military term for Command and control
C-2 (poison), developed in the Poison laboratory of the Soviet secret services

C2, UEFA Cup Winners' Cup in football, later merged with UEFA Cup (now UEFA Europa League)
C2 Pictures, a film studio
C-2 visa, a nonimmigrant visa which allows individuals to travel to and from the headquarters of the United Nations
Coca-Cola C2, a soft drink launched by The Coca-Cola Company in 2004