The myriad bodies that occur in the Solar System have a wide range of properties, from giant gaseous planets such as Jupiter to small, solid, rocky satellites such as our Moon. Exploration by spacecraft during the past four decades has shown that volcanism — an important mechanism by which internal heat is transported to the surface — is common on many of these bodies. There are many common traits; for example, relatively quiet eruptions of molten rock occur on such diverse bodies as the Earth, Mars and Jupiter's moon Io. The volcanic constructs produced, however, vary strikingly, and range from Olympus Mons on Mars, at over 20 km high, to relatively tiny cones on Earth no more than a few tens of metres high. The recognition of icy volcanoes spewing water or organic liquids on some of Saturn's moons constitutes one of the most exciting results to emerge from recent space missions.