The field of humic matter research has undergone drastic changes in concepts and principles since the first edition of Humic Matter in Soil and the Environment: Principles and Controversies was published more than a decade ago. Still the only book of its kind specifically addressing humic acid principles and controversies, the Second Edition presents the newest advances in humic acid science. Eleven new and rewritten chapters replace the original nine, with updated material representing modern humic acid chemistry. This includes the delineation of organic matter, humus, and humic matter. The book begins by considering organic matter as a whole, describing terrestrial and aquatic organic matter. It examines humus as a mixture of humified and nonhumified organic matter, focusing also on the importance of the nonhumified fraction—plant biopolymers in their original or slightly decomposed forms—as raw materials for formation of the humic fraction. The book then presents concepts of humic matter, referred to as humic acid, covering a range of ideas from traditional views of biopolymers to the latest concepts based on micellar, supramolecular, and nanotube chemistry. The author presents the major pathways of humification and discusses humification theories. He also examines the extraction, isolation, and fractionation of humic matter. The book reviews the chemical composition and model structures of humic acids, the chemical and spectroscopic characterization of humic substances, and the electrochemical properties of humic matter. It also addresses the agronomic, environmental, and industrial (including pharmaceutical) importance of humic matter. This revised and updated edition continues the tradition of providing comprehensive coverage of the genesis, extraction, properties, and impacts of humic matter.