IR

IR or Ir may refer to:

Arts and media

Iarnród Éireann (Irish Rail), national passenger and freight railway system of the Republic of Ireland
Illinois Railway, US
Indian Railways, state-owned railway company of India
InterRegio, part of Swiss Federal Railways
IR Ishikawa Railway, local railway company in Ishikawa, Japan
Iran Air (IATA airline code IR)
Israel Railways, state-owned railway company of Israel

Ingersoll Rand (NYSE trading symbol IR)
International Rectifier, a former manufacturer of power semiconductors
Independent-Republican Party of Minnesota, former name of the Republican Party of Minnesota

Incidence rate (market research)
Interest rate, or (when referring to an asset class) interest rate derivative
Information ratio, when referring to risk-adjusted returns of a financial security
Investor relations, a management responsibility in which companies disclose information for regulatory compliance and for bond/share-holders to make investment judgments

Indian Reserve, a section of land in Canada that is controlled by an Indigenous band government
Iran, by ISO country code

Immediate-release, related to time release technology in pharmaceuticals
Incidence Rate, in epidemiology
Insulin receptor, a transmembrane receptor that is activated by insulin
Insulin resistance, a pathological condition
Interventional radiology and interventional radiologist, an independent medical specialty
Inverted repeat, a sequence of nucleotides that is the reversed complement of another sequence further downstream

.ir, the Internet country code top-level domain for Iran
Adobe ImageReady, a bitmap graphics editor shipped with Adobe Photoshop by Adobe Systems
Image retention, the LCD and plasma display equivalent of screen burn
Information retrieval, the science of searching for information in or as documents or databases
Information revolution, one of the theoretical frameworks within which trends in current society can be conceptualized
Institutional repository, a digital collection for preserving the intellectual output of an institution
Institutional research, the collection, analysis, and reporting of institutional data
Instruction register, part of a CPU's control unit
Intermediate representation, a computer data structure
Internal router

Imaginary numbers, in mathematics, denoted ${\text{i}}\mathbb {R}$ or $i R$
Infrared, a portion of the electromagnetic radiation spectrum
Impulse response, an output function of a dynamic system presented with a brief input signal
Insulation resistance, a measure of insulation material performance
Ionizing radiation
Iridium, symbol Ir, a chemical element

Imperial–royal, abbreviation applied to institutions of the Austrian Empire
Industrial relations, relations between management and workers in industry
Ingenieur, abbreviated ir., an engineer's degree awarded by technical universities in the Netherlands, Belgium, Indonesia, and Malaysia
Injured reserve list, a list of professional sports players who are injured and unable to play for an extended time
International relations, in political science, the study of foreign affairs of and relations among states
International rules football a hybrid code of football