This book provides a description of the generalized two layer surface complexation model, data treatment procedures, and thermodynamic constants for sorption of metal cations and anions on hydrous aluminum oxide (gibbsite), the most common form of aluminum oxide found in nature and one of the most abundant minerals in soils, sediments, and natural waters. The book can be used in wastewater treatment. The book provides a synopsis of aluminum oxide forms and provides a clearly defined nomenclature, since there is no official universal one for this important of minerals. Compilations of available data for sorption of metal cations and anions on gibbsite are presented, and the results of surface complexation model fitting of these data are given. The book concludes with a comparison of constants extracted from data for sorption on gibbsite with those determined previously for hydrous ferric oxide (HFO) and the iron oxide goethite.