This is a comprehensive account of debris flow, describing both theoretical and applied aspects. In the first part, the fundamental mechanical characteristics are discussed, including flow characteristics, type classification, mechanics, occurrence and development, fully developed flow, and deposition processes. The second part sheds light on the application of the theories presented in computer-simulated reproductions of real disasters. Special attention is paid to debris flow controlling structures, design effectiveness and performance, soft countermeasure problems, such as the identification of debris flow prone ravines and the prediction of occurrence by means of precipitation threshold. The qualitative and fundamental character of this text makes it an excellent textbook for graduate-level courses and it is recommended reading for professionals in engineering, geosciences and water resources who are working on the mechanics and countermeasures of debris flow. The original, Japanese version of this book was awarded the 'Publishing Culture Prize' by the Japanese Society of Civil Engineers (2004).