| IRTA | Illinois Retired Teacher's Association 
| Others |
| IRTA | Independent Rear Trailing Arm
| Others |
| IRTA | Indiana Retired Teachers Association
| Others |
| IRTA | Institute for Research and Technical Assistance
| Others |
| IRTA | International Racing Teams Association
| Others |
| IRTA | International Reciprocal Trade Association
| Others |
| IRTA | International Road Racing Teams Association
| Others |
| IRTA | Intramural Research and Training Award
| Others |
| IRTA | Intramural Research Training Award
| Others |
| IRTA | Intreprinderea Regionala de Transporturi Auto
| Others |
| IRTA | Irish Real Tennis Association
| Others |
| IRTA | Irish Rider Training Association
| Others |