The Nine Planets: Io
- Overview with data, text, images, links.
- http://www.nineplanets.org/neptune.html

Io: Jupiter's Volcanic Moon
- Discussion of many geographic and geologic features of Io. Includes links, photo glossary, and a test.
- http://www.planetaryexploration.net/jupiter/io/index.html

Io During 1999
- Volcanic activity on Io during 1999 as seen from Earth.
- http://physics.uwyo.edu/~rhowell/io_1999.htm

Solarviews.com: Io
- Statistics, animations and annotated pictures.
- http://www.solarviews.com/eng/io.htm

SO2 Ice on Io
- A short scientific article about the identification of Sulfur Dioxide ice on the satellite's surface.
- http://web99.arc.nasa.gov/~astrochm/solarice.html

PIRL: Galileo Images of Io
- Many pictures from the Galileo Mission, taken between August 1999 and December 2001.
- http://pirlwww.lpl.arizona.edu/Galileo/Releases/