The book surveys volcanic phenomena, describing types of eruptions and the materials they produce, and examining the structures built around vents and the internal architecture of volcanic mountains. It discusses the distribution of volcanic activity across the globe and through geological time, and considers the sequence of operations at volcanic centres. Emphasis is placed on microscopic study of lavas and fluid inclusions, on comparisons between volcanic minerals and extraterrestrial materials, and on experiments and observations that constrain theories. The work evaluates volcanoes' roles in Earth's systems and reviews proposed causes of volcanic action, illustrated throughout with maps, diagrams, photographs, and field sketches.