This book highlights the increasing importance of humic substances in the different scientific fields related to terrestrial ecology, soil quality conservation, and environmental chemistry. It shows that modern humic substances research is not only directed to unravel their yet ill-defined chemical structure but is successfully exploring the interconnected chemical, biological, and physical processes that maintain the ecological equilibrium of soil and ensure a sustainable agricultural production. The book will primarily be of interest to soil scientists and to ecological and environmental scientists. People in the fields of forest science, agronomy, analytical and environmental chemistry, water science, environmental engineering, and coal science will also find this publication worthy of their attention.