Business:

• Illinois Railway (AAR reporting marks IR), a Class III railroad in Illinois, USA.
• Indian Railways, the state-owned railway company of India
• Industrial relations (labor relations)
• Ingénieur ("Ir"), Engineer, someone who practices the profession of engineering
• Ingersoll-Rand Company Limited (NYSE trading symbol IR)
• Integrated Resort, a euphemism for a casino in Singapore
• Internal Revenue Service, the United States government agency that collects taxes and enforces the internal revenue laws. The IRS is a bureau of the Department of the Treasury
• International Rectifier Corp., a manufacturer of power semiconductors
• International Rescue Corps, an organisation inspired by the Thunderbirds show's premise.
• Investor relations, a set of activities which relate to the ways in which a company discloses information required for regulatory compliance and good investment judgment to bond and/or shareholders and the wider financial markets
• Iran Air (IATA airline code IR)
• Irish Rail, the national passenger and freight railway system of the Republic of Ireland

Computer:

• Information Resources, sometimes used as an alternative to Information Technology
• Information retrieval, the science of searching for information in documents, searching for documents themselves, searching for metadata which describe documents, or searching within databases
• Informational Revolution, one of the theoretical frameworks within which trends in current society can be conceptualized
• Institutional repository, an online locus for collecting and preserving - in digital form - the intellectual output of an institution, particularly a research institution
• Institutional research, the collection, analysis, and reporting of institutional data
• Instruction register, refers to the part of a CPU's control unit
• Intermediate representation, a computer data structure

Fiction:

• I. R. Baboon from the cartoon series I am Weasel
• Ir, in Irish legend, was one of the sons of King Milesius who took part in a semi-legendary invasion of Ireland.
• International Rescue, the fictional rescue organization seen in Thunderbirds

Language:

• ir —city, Hebrew
• ir —to go, Spanish, Portuguese

Medicine:

• Insulin resistance
• Interventional radiology
• Ionizing radiation

Politics:

• Independent-Republican Party of Minnesota, currently known as Republican Party of Minnesota
• International relations, a branch of political science, is the study of foreign affairs of and relations among states within the international system

Science:

• Infrared, a portion of the electromagnetic radiation spectrum
• Infrared spectroscopy
• Inverted repeat, a sequence of nucleotides that is the reversed complement of another sequence further downstream
• Iridium, The 77th element

Sports:

• Injured reserve, a special sports reserve list for professional teams to use if a player is injured and unable to play for an extended time
• International Rules a hybrid code of football

Other:

• ImageReady, a bitmap graphics editor shipped with Adobe Photoshop by Adobe Systems
• Incident report
• Instrument Rating, refers to the qualifications that a pilot must have in order to fly under Instrument Flight Rules (IFR)
• Inter-racial, particularly in the Pornography industry.
• Iran (country code: IR, Internet domain: .ir)
• In Rainbows, the seventh studio album by the alternative rock band Radiohead
• Sometimes, in mathematics, IR is written in lack of a blackboard bold R ($mathbb\{R\}$), representing the real numbers.