C1

C1, C01, C.I or C-1 may refer to:

* C1, an international standard paper size defined in ISO 216 (648×917 mm)
* C1, also known as Vlakplaas, a unit of the South African Police responsible for assassinating opponents of Apartheid during the 1980s
* $C^1$, in mathematics, refers to the set of all continuously differentiable functions
* C1, a note-octave in music
* C1, a level in the Common European Framework of Reference for Languages
* C1, the code for permission to use specific land or premises for hotels, in town and country planning in the UK
* C1, the first of four pure modules taken in the GCE A Level Maths syllabus
* C1, a NRS social grade in the United Kingdom for the lower middle class
* a 2001 1.3 megapixels Olympus digital camera model
* a Yamaha grand piano model
* a class of FM radio broadcasting in North America
* C1 pylon, a type of high voltage pylon
* C1 Television, a Mongolian Television Channel
* Schecter C-1 Hellraiser FR, a guitar model

Biology

* C1, in biochemistry, refers to small molecules with one carbon atom, such as methane, methanol, formaldehyde and formate, carbon dioxide, and carbon monoxide
* C1 domain, an important secondary messenger protein domain
* C1-inhibitor, a human serine protease inhibitor
* C1 regulatory sequence for the insulin gene
* Apolipoprotein C1, a human lipoprotein
* Cytochrome C1, a precursor protein to Cytochrome C
* In human anatomy, C1 may refer to::* Cervical vertebra 1, the first cervical vertebrae of the vertebral column:* Cervical spinal nerve 1
* Complement component 1
* C02, Malignant neoplasm of base of tongue ICD-10 code
* ATC code C01, a section of the Anatomical Therapeutic Chemical Classification System

Computing

* C0 and C1 control codes defined in ISO 6429
* C1 (protocol), a 1984 protocol for file transfer, also known as "Punter"
* C-One, a single-board microcomputer
* Counter-Strike "C1", a slang expression from the video game, used to express agreement
* TCSEC C1 security class
* ATI C1, codename of the Xbox 360 GPU "Xenos"

Transport, vehicles, ships or public transport routes

* C-1 Trader, a cargo-version of the S-2 Tracker anti-submarine warfare aircraft of the United States Navy
* AEG C.I, a German World War I reconnaissance aircraft
* AGO C.I, a 1915 German reconnaissance biplane
* Albatros C.I, a 1915 German two-seat general-purpose biplane
* Aviatik C.I, a 1915 German observation plane
* Bavarian C I, a 1847 German steam locomotives class
* BMW C1, a security scooter with a roof
* Chevrolet Corvette C1, any model corvette sold from 1953 to 1962, denoted a solid-axle rearend
* Cierva C.1, a 1920 Spanish experimental autogyro
* Citroën C1, a small car
* DFW C.I, a WWI German reconnaissance aircraft
* Douglas C-1, a cargo/transport airplane produced by Douglas Aircraft for the U.S. Army Air Service starting in 1925
* Fokker C.I, a 1918 German reconnaissance biplane
* Ford C1 platform, the Ford Motor Company's global compact car automobile platform
* Friedrichshafen C.I, a 1914 German single-engined amphibious reconnaissance biplane
* GNR Class C1, a British 4-4-2 steam locomotive
* Hansa-Brandenburg C.I, a 1916 German 2-seater armed single-engine reconnaissance biplane
* HMS C1, a C-class submarine of the Royal Navy
* Kawasaki C-1, an indigenous transport aircraft of the Japanese Air Self-Defense Forces
* LB&SCR C1 class, a 1882 British freight steam locomotive
* London Buses route C1
* NER Class C1, a British 0-6-0 steam locomotive
* Nimrod NRA/C1, a 1981 test design racing car
* PRR C1, an American
* Rumpler C.I, a 1915 German two-seater single-engine reconnaissance biplane
* Sauber C1, a
* SP&S Class C-1, a steam locomotives class
* Type C1 ship, a small cargo vessel built by the United States in large numbers before and during World War II
* USS C-1 (SS-9), a C-class submarine of the United States Navy
* USS Newark (C-1), a protected cruiser of the United States Navy
* Claro M. Recto Avenue, a road in Metro Manilla, Philippinesand also :
* 'C1', the numberplate of the Prime Minister of Australia's official VIP transportation
* The One-way traffic sign, from the Vienna Convention on Road Signs and Signals

ports

* C1, an abbreviation for single-person Sprint Canoe
* 'C1', the top category in Group C sportscar racing, used between 1985 and 1990
* C1, the UEFA Champions League (formerly known as the European Cup) in football
** Supercoppa di Lega Serie C1 in Italy