This text covers the emerging research field of naturally occurring gas hydrates (focusing on methane hydrate). It is not primarily a physical chemistry textbook. This book is designed as a broad introduction to the field of hydrate science, demonstrating the significance of the hydrate cycle to energy resource potential, seafloor stability, and global climate and climate change, along with other issues. The best known hydrate localities are described, as are research and laboratory methods and results. The book consists of chapters grouped in related themes that present up-to-date information on methane hydrate. Each of the contributing authors is expert in hydrate science and most have been carrying out research in hydrate for a considerable time.