| Acronym | Definition |
|---|
| IRS | Internal Revenue Service (US government) |
| IRS | Insulin Receptor Substrate |
| IRS | Indoor Residual Spraying (mosquito control) |
| IRS | Independent Rear Suspension |
| IRS | Interest Rate Swap |
| IRS | Indian Remote Sensing Satellite |
| IRS | Infrared Spectrograph |
| IRS | Insulin Resistance Syndrome |
| IRS | Information Retrieval System |
| IRS | Indian Register of Shipping (Indian ship classification society) |
| IRS | Imposto Sobre o Rendimento das Pessoas Singulares (Portuguese tax) |
| IRS | Inertial Reference System |
| IRS | Incident Reporting System |
| IRS | Interface Requirements Specification |
| IRS | Information Referral Services (Ontario, Canada) |
| IRS | Information Reporting System |
| IRS | Increasing Returns to Scale |
| IRS | Indian Revenue Service (India) |
| IRS | Investor Relations Society |
| IRS | International Register of Shipping (est. 1993; shipping industry) |
| IRS | Inventory Reduction Sale |
| IRS | Irwin R. Schyster (pro wrestler) |
| IRS | Internal Review Service (UK) |
| IRS | International Radar Symposium |
| IRS | Institute of Regional Studies (Pakistan government) |
| IRS | Intelligence Research Specialist (FBI) |
| IRS | Integrated Resorts Scheme (Mauritius) |
| IRS | Informal Resolution System |
| IRS | International Referral System (now INFOTERRA) |
| IRS | Inherited Runners Scored (baseball; runner on base who scores after a new pitcher enters) |
| IRS | Intel Research Seattle |
| IRS | International Rorschach Society |
| IRS | Illinois Radiological Society |
| IRS | Interest Rate Support |
| IRS | Infrared Locking System (automobiles) |
| IRS | Internationally Recruited Staff |
| IRS | Intermediate Reference System |
| IRS | International Research and Studies Program (US) |
| IRS | Intelligent Register System (Q.I. Press Controls) |
| IRS | Industrial Relations Survey (UK) |
| IRS | Information Receiving Station |
| IRS | Infrared Soldering |
| IRS | Ionizing Radiation Standards Group (National Research Council of Canada, Ottawa, Canada) |
| IRS | Interstate Repeater Society |
| IRS | I'll Return Shortly |
| IRS | Ignition Radiation Suppression |
| IRS | Incident Response Service |
| IRS | Inland Refugee Society (Vancouver, British Columbia, Canada) |
| IRS | Indian Remote Sensing System |
| IRS | Index of Retail Saturation |
| IRS | International Reference Star (set of star catalogs) |
| IRS | Item Reduction Study |
| IRS | Interferometric Rayleigh Scattering |
| IRS | Input Record Seperator (Perl programming language) |
| IRS | Increasing Radius Search |
| IRS | Imagery Requirements Structure |
| IRS | Individual Readiness Survey (education) |
| IRS | Infrastructure Requirements Specification |
| IRS | Interference Reduction System |
| IRS | Institute of Railway Signal Engineers (UK) |
| IRS | Infrared Suppressor |
| IRS | Indiana Railroad System |
| IRS | Indefinite Reserve Status |
| IRS | Induction and Recruiting Station |
| IRS | Installation Readiness System |
| IRS | Institute for Reactor Safety, Germany (now Gesellschaft für Anlagen- und Reaktorsicherheit mbH) |
| IRS | Integrated Resource and Schedule |
| IRS | International Racing System |
| IRS | Integrated Review Software |
| IRS | International Russian Society |
| IRS | Integrated Reconstructed Spectrum |
| IRS | Inferno Reckless Summonn (Yu-Gi-Oh) |
| IRS | Individual Research Study |
| IRS | Impulse Radio Sequence |
| IRS | International Reply Service |
| IRS | Immune Reconstitution Syndrome |
| IRS | Investment Research Service |
| IRS | Interactive Response System (educational remote control) |
| IRS | Image Retrieval System (computing) |
| IRS | Insulin Receptor Signaling |
| IRS | Identical, Related and Similar (US DHHS) |
| IRS | Intra Renal Surgery |