| Term | Definition |
|---|---|
| GSFC | Goddard Space Flight Center, USA |
| IAA | Institute of Applied Astronomy, Russia |
| IAG | International Association of Geodesy |
| IAU | International Astronomical Union |
| ICRF | International Celestial Reference Frame |
| IDS | International DORIS Service |
| IERS | International Earth rotation and Reference frames Service |
| IGN | Institut National de l'Information Géographique et Forestière, France |
| IGS | International GNSS Service |
| ILRS | International Laser ranging Service |
| INASAN | INstitut AStronomii rossijskoj Akademii Nauk (Institut of Astronomy of the Russian Academy of Sciences), Russia |
| IRD | Institut de Recherche pour le Développement (ex-ORSTOM), France |
| ISGN | International Space Geodetic and Gravimetric network |
| ITFS | International Terrestrial Frame Section |
| ITRF | International Terrestrial Reference Frame |
