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Most of our knowledge of Ganymede comes from the flybys by the Voyager and Galileo missions. Although Pioneer 10, and 11 passed through the Jovian system in the 1973 neither provided much information on Ganymede. Various proposals have been made for future missions. The extremely ambitious Jupiter Icy Moons Orbiter has been recently canceled.
 Voyager 1 & 2 launched 1977
 The Voyager probes photographed the Jovian system throughout the first half of 1979. The Voyager probes sent back the first close up images of Ganymede in 1979, showing a 'dirty iceball'. This resulted in a massive rethinking of the moon's likely geology from something similar to Luna, to the current model with a global ocean under the ice.
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Galileo launched 1989
 The space probe Galileo detected a magnetic field around Ganymede in 1996; this suggests it may have a molten core. Galileo photographed Ganymede at a distance of 7,448 km/4,628 mi. The resulting images were 17 times clearer than those taken by Voyager 2 in 1979. Ganymede's subsurface ocean is now generally accepted as a result of Galileo's findings.
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Juno planned 2010
 Juno is a NASA mission to Jupiter planned to cost roughly $700 million and scheduled to launch by June 30, 2010. The spacecraft will be placed in a polar orbit in order to study the planet's magnetic field. Juno will also be searching for evidence that Jupiter has a rocky core, the amount of water present within the atmosphere, and Jupiter's wind (which can reach speeds of 600 km/h). It will be the first mission to Jupiter relying on solar (not nuclear) energy. Juno should be able capture information on the Galilean moons polar reagions.
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