| Acronym | Definition |
|---|
| SIR | School of International Relations (Iran) |
| SIR | Society of Interventional Radiology |
| SIR | Staten Island Railway (NY, formerly SIRT, Staten Island Rapid Transit) |
| SIR | Self-Insured Retention |
| SIR | Summary Information Return |
| SIR | Spaceborne Imaging Radar |
| SIR | Social Information Retrieval (various organizations) |
| SIR | Scholar in Residence |
| SIR | Social Indicators Research (various organizations) |
| SIR | Shooting Incident Reconstruction (forensics) |
| SIR | Security Intelligence Report (Microsoft threat analysis) |
| SIR | Safety Information Registration |
| SIR | Secondary Image Registration |
| SIR | Security Intelligence Report |
| SIR | Standard Infra Red |
| SIR | Save Instruction Recognition |
| SIR | Serial Infra Red |
| SIR | Standardized Incidence Ratio |
| SIR | Serial Infrared |
| SIR | Signal-to-Interference Ratio |
| SIR | Short Interest Ratio (finance) |
| SIR | Surface Insulation Resistance |
| SIR | Shuttle Imaging Radar |
| SIR | Savings-to-Investment Ratio |
| SIR | Statistical Inventory Reconciliation |
| SIR | Specific Information Requirement (US DoD) |
| SIR | Statement of Intent to Register (College) |
| SIR | Screening Information Request (US FAA; same as RFP) |
| SIR | Supplemental Inflatable Restraint |
| SIR | Silent Information Regulator |
| SIR | Serious Incident Report |
| SIR | Single Instance Repository |
| SIR | Statutory Invention Registration |
| SIR | Society of Insurance Research |
| SIR | Singapore Infantry Regiment |
| SIR | Seattle International Raceway |
| SIR | Special Investment Region (Dholera, Gujarat, India) |
| SIR | System Impedance Ratio (power systems) |
| SIR | Susceptible-Infected-Removed |
| SIR | Social Investigation Report (Juvenile Justice Act; India) |
| SIR | Société Ivoirienne de Raffinage (Abidjan, Ivory Coast) |
| SIR | Security Incident Report |
| SIR | Southeastern Institute of Research (ad survey firm) |
| SIR | Starting Independent Researcher (European Research Council grant) |
| SIR | Standard Indonesian Rubber |
| SIR | Specific Insulation Resistance (electrical engineering) |
| SIR | Sons In Retirement (Northern California retired men's luncheon club) |
| SIR | Scientific Information Retrieval |
| SIR | Selected Ion Recording (mass spectrometry) |
| SIR | Singapore Immigration and Registration |
| SIR | Statistical Information Retrieval |
| SIR | Safeguards Implementation Report |
| SIR | Stepped Impedance Resonator |
| SIR | Speech Intelligibility Rating |
| SIR | Safety Investigation Report |
| SIR | Sequential Importance Resampling |
| SIR | Sigma Iota Rho (international studies honorary society) |
| SIR | Single Interactive Repository (computing) |
| SIR | System Investigation Request |
| SIR | Session Initiation Request |
| SIR | Sample Inspection Report (engineering prototype) |
| SIR | Snow and Ice on Runway |
| SIR | Selective Integrated Rail System (law enforcement product) |
| SIR | Supervised Intensive Restitution (Alabama prison program) |
| SIR | Sorry If Repost |
| SIR | Simulated Intelligence Robotics |
| SIR | System Integration Review |
| SIR | Spatial Impulse Response |
| SIR | System Incident Report |
| SIR | Submarine Intermediate Reactor |
| SIR | Service Information Request |
| SIR | Switched Integrated Rectifier (three phase transformer-rectifier power supply) |
| SIR | Simple Indexing and Retrieval |
| SIR | Standard Information Retrieval unit |
| SIR | Systems Integrated Research (UK educational software firm) |
| SIR | Standard-Issue Information Retrieval Unit (Invader Zim) |
| SIR | Smooth Interpersonal Relationship |
| SIR | Supplier Information Request |
| SIR | Source Initiated Reservation |
| SIR | Society of Individual Rights (1960s San Francisco homophile group) |
| SIR | Scheduled Inspection and Repair |
| SIR | Skill Independent Regional (Visas) |
| SIR | Site Inspection Request |
| SIR | Service Implementation Repository |
| SIR | Semiannual Inventory Report |
| SIR | Software Incident Report |
| SIR | Smith Industrial Rubber |
| SIR | Sooner International Raceway |
| SIR | Sensitive, Intermediate, Resistant |
| SIR | Safety Interlock Relay |
| SIR | Sveriges Inredningsarkitekters Riksförbund |
| SIR | Set Iron Rod |
| SIR | Society of Independent Representatives Inc |
| SIR | Search, Inspection & Recovery |
| SIR | Special Inspection Requirement |
| SIR | Stored Information Retriever |
| SIR | Sequential Independent Reviews |
| SIR | Supervisor Investigation Reports (insurance) |
| SIR | Surveillance Information Retrieval (gaming) |
| SIR | Special Investigative Requirement |
| SIR | Scramble Intercept Recovery |