CI or Ci may refer to:

Business terminology

* Commercial invoice * Competitive intelligence * Confidential information * Continual improvement * Corporate identity * Customer intelligence, a discipline in marketing

Businesses and organisations

Academia and education

* California State University, Channel Islands * Channel Islands High School * Collegium Invisibile * Confucius Institute

Religion

* Josephites of Belgium, a Catholic congregation * Christian Identity * Christian Institute, a British charity which promotes Christian values

Other businesses and organizations

* CI Financial, Canadian investment management company * Charity Intelligence Canada * China Airlines (IATA code) * Cigna health services (NYSE symbol) * Consumers International * Cycling Ireland * CI Records, a music record label * Cambria and Indiana Railroad * CANZUK International, organisation which promotes cooperation between Canada, Australia, New Zealand and the United Kingdom * Conservation International, an international environmental non-governmental organization * Communications International, a former global union federation * Communist International * Children International, a non-profit child sponsorship organization * Cryonics Institute, American nonprofit foundation

Law and military

* Counterintelligence * Confidential informant * Compliance Inspection, a United States Air Force inspection * Chief inspector, a police rank * Circle inspector, a junior police rank * Certificate of identity * Civilian Internee, a special status of a prisoner during wartime * Civilian Instructor, an adult volunteer in the British Air Training Corps#Civilian instructors and chaplains, Air Training Corps and Royal Canadian Air Cadets, Canada Air Cadets

Places

* Ci County, in Hebei, China * Cayman Islands * Chile (FIPS country code, obsolete NATO country code) * Coney Island * Cocos (Keeling) Islands, an external territory of Australia * Cook Islands, an island-country in the South Pacific Ocean * Côte d'Ivoire (ISO country code) * Channel Islands * Channel Islands of California * Carbonia-Iglesias, a province in southern Italy * Central India, region of India, abbreviated CI ** Central India Circuit or C. I. Circuit, a Hindi film distribution circuit comprising parts of Madhya Pradesh (Indian state within central India)

Science, technology and mathematics

Biology and medicine

* cI protein, a repressor protein of ''Enterobacteria phage λ'' * Cytoplasmic incompatibility, a reproductive system * Cardiac index * Ci protein, Cubitus interruptus -protein * Coital incontinence * Convergence insufficiency * Corpulence index * Cumulative incidence, used as a measure of disease frequency in epidemiology * Cochlear implant * Chemical injury syndrome, an increased sensitivity to common chemicals also called multiple chemical sensitivity. * Chronic illness, a condition that is long-lasting or recurrent * Contraindication

Computing

* .ci, the Internet country code top-level domain (ccTLD) for Côte d'Ivoire * Common Interface, for a Conditional Access Module ** CI+, Common Interface Plus * Computational intelligence * Configuration item, the fundamental structural unit of a configuration management system * Core Image, non-destructive image processing technology * Continuous integration, a software-engineering practice of merging developer code into a main code base frequently * CodeIgniter, a PHP framework

Earth science

* Cirrus cloud * Convective instability

Mathematics

* Conditional independence, a type of relation of random variables in probability theory * Confidence interval, an interval estimate of a population parameter used in statistics * 101 (number) (in Roman numerals) * Compound interest * Cosine integral (standard mathematical symbols "Ci" and "ci")

Physics

* Conical intersection, the location of a discrete degeneracy between two electronic states * Curie (unit) (Symbol: Ci), a measurement of radioactivity named after Marie Curie * Copenhagen interpretation, an interpretation of quantum mechanics * Cubic inch, a unit of volume

Other uses in science and technology

* CI group, a type of Carbonaceous chondrite#CI group, carbonaceous chondrite meteorite * Carrier interferometry, a radio and optical communication coding technology * Chemical ionization, a technique used in mass spectrometry * Configuration interaction, a post-Hartree–Fock method used in computational chemistry * Contextual inquiry, a user-centered design research method * Collective intelligence, a subfield of sociology * Colour Index International, a reference database of CI numbers for dyes and pigments * Bavarian C I, a steam locomotive with the Royal Bavarian State Railways * Compression ignition engine, another name for a diesel engine

Television

* ''Canadian Idol'', a Canadian television series * ''Law & Order: Criminal Intent'', an American television series * Crime & Investigation Network ** Crime & Investigation Network (Australia), Australian cable and satellite network focusing on Crime ** Crime & Investigation Network (Europe), a pan-European television channel ** Crime & Investigation Network (South East Asia)

Other uses

* Ci (poetry), a form of Chinese lyric poetry * Qi, a central concept in several eastern philosophies * Categorical imperative, in philosophy * Colour Index International, a reference database * Comprehensible input * Contact improvisation, a dance technique * CI, postnominal for Companion of the Order of the Crown of India * Ci, a form of the surname Qi (surname), Qi, of the Tungusic peoples