C4

C4, C04, C.IV or C-4 may refer to:
* C4 (Colombia), a political party in Colombia
* C-4 (explosive), a type of plastic explosive

In biology:
* C4 carbon fixation, a pathway for carbon fixation in photosynthesis
* ATC code C04, section of the Anatomical Therapeutic Chemical Classification System
* In human anatomy, C4 may refer to::* Cervical vertebra 4, one of the cervical vertebrae of the vertebral column:* Cervical spinal nerve 4
* Apolipoprotein C4, a human gene
* Complement component 4, a protein
* C04, Malignant neoplasm of floor of mouth ICD-10 code

In vehicles:
* C-4, the US Army designation of the Ford Trimotor
* a class of Audi 100 and Audi A6
* C-4 Academe, the military version of Gulfstream I twin turboprop business aircraft
* AEG C.IV, a German World War I reconnaissance aircraft
* AGO C.IV, a 1917 German reconnaissance aircraft
* Bavarian C IV, a 1884 German steam locomotive
* Chevrolet Corvette C4, the fourth production design of the Chevrolet Corvette
* Cierva C.4, a 1922 Spanish experimental autogyro
* Citroën C4, a car made by Citroën
* DFW C.IV, a 1916 German reconnaissance aircraft
* Fokker C.IV, a 1923 Dutch two-seat reconnaissance aircraft
* Ford C4 transmission, an automatic transmission
* GS&WR Class C4, a Great Southern and Western Railway
* HMS C4, a British C class submarine of the Royal Navy
* Menasco C4, a 1930s 4-cylinder, air-cooled, in-line, inverted, aero-engine
* Rumpler C.IV, a 1917 German single-engine, two-seater reconnaissance biplane
* Saturn C-4, a 1960 conceptual American launch vehicle
* Sauber C4, a
* Spyker C4, a car
* USS "C-4" (SS-15), a United States C class submarine of the United States Navy
* USS "Philadelphia" (C-4), a protected cruiser of the United States Navy
* Canadair North Star C-4 aircraft derived from the Douglas DC-4

In paper:
* C4, an international standard paper size (229*324 mm), defined in ISO 216
* C4, the envelope size matching the A4 paper size

In computing:
* Cx4 chip, an add-on microprocessor chip for the Super Nintendo system (often incorrectly referred to as the "C4 chip")
* Flip chip packaging is also called Controlled Collapse Chip Connection, or C4
* VIA C4, a planned design of central processing unit for a personal computer
* C4 (conference), a Macintosh software developers conference
* C4 Engine, a next-generation 3D game engine
* CodeWeavers CrossOver Compatibility Center
* Suneido programming language is the successor language to the C4 programming language from Axon Development Corporation

In music and television:
* Channel 4, a United Kingdom television broadcaster
* C4 (TV channel), a New Zealand television music channel
* Middle C in music (American notation)
* c4 - Musical note, C above high C - European notation
* C-4 (rapper)
* C4 Records, a record label
* C-4 (punk rock band) A racist punk band from Columbia, MO
* C4 (band), a neo-classical metal band set up by Michael Angelo Batio
* C4 & some Saxophones (sax quartet) a Saxophone quartet from Potsdam, NY.

In sports
* C4, an abbreviation for a four-man Sprint Canoe
* C4, a term used to refer to the UEFA Intertoto Cup, a football competition, so named because it was (until 1999) the fourth most prestigious UEFA competition. Mainly used in non-English speaking countries

In chess
* 1. c4, also called the English Opening, is the fourth most popular chess opening.

Other:
* C4, an acronym for "Command, Control, Communications, and Computers", used by the US Department of Defense
* C4 (heraldry), the monogram of Christian IV of Denmark, used in the city arms of Kristianstad, Sweden since 1622
* C4, the IATA code for Zimex Aviation Limited
* C-4, professional wrestler Paul Burchill's name for his finishing move, a moonsault uranage
* C4 (Belgium), form from the employer entitling an employee to claim unemployment benefits at the end of employment
* C4, or CIV: Star Wars Celebration IV, held in Los Angeles
* Churches Covered and Connected in Covenant, a Religious Association founded by Archbishop LeRoy Bailey Jr.
* butyl-type hydrocarbon chain with 4 carbon atoms, especially in C4 reversed-phase chromatography columns