Volcanic eruptions are one of the most dangerous and volatile geological hazard. In the 20th Century, almost 100,000 people are believed to have been killed in volcanic eruptions, with another 4.7 million directly affected by them, but, at the end of the 20th century, over 500 million people lived within the hazard zone of a volcano worldwide; cities such as Tokyo, Mexico City, Naples and Seattle are besieged by the threat of nearby volcanoes. Volcanoes also provide fertile soils, near-unlimited geothermal power generation potential and are an intricate part of the Earth system. This course aims to study the mechanism through which volcanoes form on Earth and other rocky planets, the circumstances that trigger eruptions, the processes which cause eruptions to change and evolve, and their impact on our society.