CIR may refer to:
- Caledonian Road & Barnsbury railway station, the standard code for this railway station
- Carbon Isotope Ratio analysis, a subset of isotope ratio mass spectrometry
- Carrier-to-interference ratio or Signal:Interference ratio, a term used in radio transmission
- Center for Individual Rights, an individual rights protection group
- Central Ischaemic Response, a cause of fainting, see Syncope (medicine)#Causes
- Christmas Island Resort
- Combustion Integrated Rack, an International Space Station microgravity research tool
- Command Instrument Rating, a category of aircraft pilot Instrument Rating
- Commissioner of Internal Revenue, a US Treasury position
- Committed Information Rate, a synonym for minimum guaranteed bitrate in telecommunications
- Committee on International Relations (University of Chicago), a graduate program
- Committee on International Relations, the name of the United States House Committee on Foreign Affairs prior to 2007
- CIR Group, Compagnie Industriali Riunite an industrial holding company of the De Benedetti Group
- Component Infrastructure Roadmap, a computer systems service-oriented architecture
- Comprehensive Immigration Reform Act of 2006, a US Senate Bill on border security
- Comprehensive Immigration Reform Act of 2007, full name: Secure Borders, Economic Opportunity and Immigration Reform Act, a US Senate Bill
- Consumer IR, infrared remote control and communication
- Coordinator for International Relations, a position within the JET Program
- Corotating Interaction Region, the interface between fast and slow regions of the solar wind
- Cosmetic Ingredient Review, a consumer safety group
- Cost:Income Ratio, one of a series of financial ratios
- Cox–Ingersoll–Ross model for interest rate dynamics
- Circinus (constellation), written Cir, a standard astronomical abbreviation
- Channel 1 Releasing, an adult film studio
- The Campionato Italiano Rally the official title of the Italian Rally Championship.