C11

C11, C.XI, C-11 or C.11 may refer to:

Transport

 * C-11 Fleetster, a 1920s American light transport aircraft for use of the United States Assistant Secretary of War
 * Fokker C.XI, a 1935 Dutch reconnaissance seaplane
 * LET C-11, a license-build variant of the Soviet Yakovlev Yak-11 trainer aircraft
 * C-11 Gulfstream II, the military designation of the Gulfstream II business jet
 * Barroso (C11), a light cruiser of the Brazilian Navy
 * HMS C11, a 1907 British Royal Navy C class submarine
 * HMS Liverpool (C11), a 1937 British Royal Navy Town class light cruiser
 * JNR Class C11, a class of Japanese steam locomotives
 * USS Marblehead (C-11), an 1892 light cruiser of the United States Navy
 * BSA C11, a British motorcycle manufactured between 1939 and 1956
 * Mercedes-Benz C11, a 1990 Group C prototype race car
 * London Buses route C11, a public transportation route in England
 * LNER Class C11, a class of British steam locomotives
 * Leapmotor C11, a mid-size electric crossover SUV

Science and technology

 * C11 (C standard revision), standardized version of the C programming language
 * Head and neck cancer (ICD-10 code)
 * Eye diseases, (MeSH code); see List of MeSH codes (C11)
 * Carbon-11, an unstable isotope of the chemical element Carbon
 * Caldwell 11, the Bubble Nebula, an emission nebula in the constellation Cassiopeia

Other uses

 * C11 (rifle), a competition and training weapon used by members of the Royal Canadian Army Cadets
 * C11 Right of Association (Agriculture) Convention, 1921
 * Bill C-11, various articles of legislation of the Parliament of Canada
 * French Defence (Encyclopaedia of Chess Openings code)
 * 11th century