C3

C3, C-3, C.3, C03, C.III or C-III may refer to:

Life and biology

 * C3 carbon fixation in plants
 * C3-convertase, an enzyme
 * Complement component 3, a protein of the innate immune system
 * Apolipoprotein C3, a human very low density lipoprotein
 * ATC code C03 Diuretics, a subgroup of the Anatomical Therapeutic Chemical Classification System
 * Castavinol C3, a natural phenolic compound found in red wines
 * Cytochrome-c3 hydrogenase, an enzyme
 * Haplogroup C-M217, called C3 in older publications
 * In human anatomy, C3 may refer to:
 * Cervical vertebra 3, one of the cervical vertebrae of the vertebral column
 * Cervical spinal nerve 3
 * Clinical Cell Culture, a medical technology company
 * C03, Malignant neoplasm of gum ICD-10 code
 * C3 Collaborating for Health, a health-promotion NGO
 * C3: an EEG electrode site according to the 10-20 system

Military

 * C3, Command, control, and communications, a military concept
 * C-3 (plastic explosive), a plastic explosive related to C4
 * C-3, a United States military designation for the Ford Trimotor
 * the designation for several German World War I and World War II armed reconnaissance aircraft
 * AEG C.III
 * AGO C.III, a reconnaissance biplane of World War I
 * Albatros C.III
 * DFW C.III, a DFW aircraft
 * NAG C.III, an engine powering the Gotha G.IV aircraft
 * C-3, a U.S. military transport version of the Martin 4-0-4
 * Type C3 submarine (disambiguation), a World War II Imperial Japanese Navy cargo carrier submarine
 * Spanish submarine C-3
 * HMS C3, a 1906 British C class submarine
 * Type C3-class ship, a type of merchant cargo ships of United States Maritime Commission "C" design
 * USS C-3 (SS-14), a 1909 United States C class submarine
 * USS Baltimore (C-3), an 1888 protected cruiser of the United States Navy
 * Garda Crime and Security Branch (CSB), domestic security agency of Ireland's national police, also known as "C3"
 * C3 Howitzer, a lengthened variant of the M101 used by the Canadian Armed Forces

Technology

 * C3, characteristic energy, in astrodynamics, a measure of the rocket energy for an interplanetary mission that requires attaining an orbital velocity above escape velocity
 * C3, the chemical symbol for
 * Tricarbon
 * Cyclopropatriene
 * C3.ai, an AI company founded by Thomas Siebel
 * C3 linearization, a computer science algorithm for resolving the order of method resolution in multiple inheritance conditions
 * Delfi-C3, a Dutch CubeSat satellite
 * Saturn C-3, a 1960 rocket in the Saturn C series
 * Chaos Communication Congress, the biggest annual hacker event in Europe
 * Chrysler Comprehensive Compensation System, important in the development of Extreme Programming
 * VIA C3, a computer processor
 * Creatures 3, a 1999 video game
 * Crysis 3, a 2013 video game
 * Cluster 3, also known as Samba, an ESA satellite

Transportation

 * Aeronca C-3, an American airplane
 * Bavarian C III, a German steam locomotive model
 * Bavarian C III (Ostbahn), an 1867 German steam locomotive model
 * Chevrolet Corvette (C3), the third production design of the Chevrolet Corvette
 * Circumferential Road 3 or C-3, an arterial road of Manila, Philippines
 * Cierva C.3, a 1921 Spanish experimental autogyro
 * Citroën C3, a car
 * Cowin C3, a car
 * LB&SCR C3 class, a British LB&SCR locomotive
 * London Buses route C3, a Transport for London contracted bus route
 * C3 (railcar), a bi-level railcar built by Kawasaki Railcar for the non-electrified branches of the Long Island Rail Road
 * Nimrod NRA/C3, a 1983 Group C racing car never achieved
 * Yamaha C3, a 2007 liquid cooled 49cc four-stroke motor scooter
 * Two different ring expressways in Japan that are numbered C3:
 * Tokyo Gaikan Expressway in Tokyo, Saitama and Chiba Prefectures
 * Tōkai-Kanjō Expressway in Aichi, Gifu and Mie Prefectures

Music

 * Hammond C3 organ
 * High C in music (c3 in European notation)
 * Low C in music (C3 in American notation)
 * Tha Carter III, the title of an album by rapper Lil Wayne
 * C3 Presents, independent American concert promoters

Other uses

 * C3 (classification), a para-cycling classification
 * C-3, Nickelodeon's old name
 * C3 (light novel), a 2011 Japanese light novel series and anime by Hazuki Minase
 * C3, a New Zealand logistics company owned by Linx Cargo Care Group
 * C3, the code for permission to use specific land or premises for dwellings in town and country planning in the United Kingdom
 * C3, the UEFA Europa League in football
 * C3, a standard paper size defined in ISO 216
 * Tippmann C-3, a pump-action paintball marker that uses propane gas
 * C3 Church Global, a worldwide Pentecostal denomination
 * C3, a class in FM radio broadcasting in North America
 * Argus C3, a 35mm rangefinder camera
 * Nokia C3 (disambiguation), various Nokia cellphones
 * Caldwell 3 (NGC 4236), a barred spiral galaxy in Draco
 * C3 policing, a methodology being employed by police to combat gangs in Springfield, Massachusetts
 * Nielsen ratings that include recorded programs watched three days later
 * Championing Community Children, a Philippine charitable organization abbreviated as C3
 * Charles Keating III (born 1955), American former swimmer and real estate executive
 * Charles III (born 1948), King of the United Kingdom and 14 other Commonwealth realms since 2022.
 * C-III Capital Partners, an asset management and commercial real estate services company
 * Hexadecimal number C3 (decimal 195)