Tannins are astringent, bitter plant polyphenols that either bind and precipitate or shrink proteins and various other organic compounds including amino acids and alkaloids. The astringency from the tannins is what causes the dry and puckery feeling in the mouth following the consumption of unripened fruit or red wine. This book presents current research in the study of tannins including: the effect of tannins in animal nutrition; proanthocyanidins in grapes and wines; using tannins to produce coagulant agents for water purification; and solar photodegradation of tannin in wood leachate.