- Jackson School of Geosciences
- Jackson State University
- Jacobs Technology ESCG
- Jacobs University = Constructor University [Bremen]
- Jaicoa Observatory
- James Franck Institute
- Japan Aerospace Exploration Agency [Sagamihara]
- Japan Aerospace Exploration Agency [Tokyo]
- Japan Aerospace Exploration Agency [Tsukuba]
- Japan Agency for Marine-Earth Science and Technology
- Japan Atomic Energy Agency [Ibaraki]
- Japanese National Observatory
- Japan Meteorological Agency
- Japan Science and Technology Agency
- Japan Society for the Promotion of Science
- Jawaharlal Nehru University
- Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy [Preston]
- Jet Propulsion Laboratory
- J. Heyrovský Institute of Physical Chemistry of the ASCR
- Jinan University [Guangzhou]
- Johannes Gutenberg - Universität Mainz = Johannes Gutenberg University
- Johns Hopkins University
- Johns Hopkins University Applied Physics Laboratory [Laurel, MD]
- Johns Hopkins University School of Medicine [Baltimore]
- Joint Center for Earth Systems Technology [Baltimore]
- Joint Global Change Research Institute
- Joint Institute for High Temperatures of the RAS
- Joint Institute for Laboratory Astrophysics
- Joint Institute for the Study of the Atmosphere and Ocean
- Joint Institute for VLBI in Europe
- Joseph Louis LAGRANGE
- JRC Institute for Energy and Transport
- JRC Institute for Environment and Sustainability
- Jucar River Basin Authority
- Jülich Supercomputing Centre
- Julius-Maximilians-Universität Würzburg = University of Würzburg
- Jupiter Intelligence
- JUPOS - Database for Object Positions on Jupiter
- Justus-Liebig-Universität Gießen = Justus Liebig University