Humic substances are highly-abundant organic compounds formed in soils and sediments by the decay of dead plants, microbes and animals. This book focuses on the important binding properties of these compounds which regulate the chemical reactivity and bioavailability of hydrogen and metal ions in the natural environment. Topics covered include the physico-chemical properties of humic matter and interactions of protons and metal cations with weak acids and macromolecules. Experimental laboratory methods are also discussed, together with mathematical modelling. Finally the author looks at how the results of this research can be used to interpret environmental phenomena in soils, waters and sediments. This comprehensive account of cation binding by humic matter is a valuable resource for advanced undergraduate and graduate students, environmental scientists, ecologists and geochemists.