IAU | International Astronomical Union |
ICS | International Commission on Stratigraphy |
ICTF | International Commission on the Taxonomy of Fungi |
ICZN | International Commission on Zoological Nomenclature |
| International Committee on Bacteriological Nomenclature |
ICTV | International Committee on Taxonomy of Viruses |
| International Hydrographic Organization |
IISE | International Institute for Species Exploration |
IMA | International Mineralogical Association |
IMA | International Mycological Association |
| International Society for Plant Pathology (13 Jan 2010 - ) |
IUCN | International Union for Conservation of Nature (1948 - ) |
IUCN | International Union for Conservation of Nature and Natural Resources (1948 - ) |
IUPAC | International Union of Pure and Applied Chemistry |