Why is this book needed? What is its rationale? The study of volcanoes and volcanic activity is an essential component of all introductory geology courses. Although the typical exposure to volcanology is superficial in most introductory courses, advanced undergraduate courses and specialized graduate courses require authoritative textbooks on volcanology either for reference, or as the backbone of focused courses and seminars. We believe our book would best serve college-level students poised to enter the earth sciences professionally, and will also serve as an important reference for interested lay readers and earth scientists in general. Volcanoes are a vital presence in our world, and play a key role in maintaining the human eco-environment through soil enrichment and atmospheric inputs. They are also hazardous features, whose eruptions have not only killed many hundreds of thousands of people in recorded history, but have also greatly influenced both the development of human culture and the evolution of human species. Volcanoes commonly form beautiful landscapes, and form the principal features of national parks all over the world, serving as magnets that attract millions of visitors each year. Hundreds of millions of other people live on or in the shadows of active volcanoes. Most of these people have only a shallow, passing interest in the volcanoes they see, but there is a certain large, enthusiastic cohort of these people whose fascination with volcanoes leads them travel to see volcanoes close-up, and to seek authoritative volcanological information.