Volcanoes are one of the world’s most important natural phenomena. But why do they exist, and what explains their peculiar distribution? Why do they display such a variety of forms and vary so much in the threats that they pose to humanity? Is any place on Earth’s surface truly “safe” from volcanic eruptions? And is Planet Earth in some way special because of its volcanoes? If so, what do they teach us about our terrestrial home? These fundamental questions about volcanoes have intrigued (and frightened!) people for millennia, and we have learned much in the past fifty years of exploration to address each, scientifically. In fact, some of the emergent reality actually surpasses mythology and fiction in the fantastic picture it portrays.