Objective: To capture current information on the role of tannins in soils and ecosystems and their implications for agricultural and environmental issues. •Tannins (or polyphenolic compounds) are of interest in food chemistry, human and animal nutrition, industrial applications, environmental soil science, and agronomy. •Topics to be covered include basic to practical knowledge of –tannin chemistry, –tannin quantification, –metal-tannin interactions, –role of tannins from the (1) soil chemical, (2) ecological, and (3) environmental points of view.