This book reviews recent research and applications of chitin and chitosan, as natural alternatives of fossil fuel products, in medicine and pharmacy, agriculture, food science and water treatment. Chitin and chitosan products are polysaccharides derived from food waste of crustaceans and fungi, and thus are cheap, abundant, sustainable, non-toxic, recyclable and biocompatible. Remarkable applications include food additives and preservation, packaging materials, biopesticides and fertilisers, drug delivery, tissue engineering, bioflocculation and dye removal.