Chitin is a naturally abundant polysaccharide and the supporting material of crustaceans (such as crabs, shrimps and cuttlefish), insects, and fungi. Chitin is the second most abundant natural polymer after cellulose and estimated to be produced annually almost as much as 10 billion tons. It is a highly insoluble material resembling cellulose in its solubility and low chemical reactivity.Chitosan is the modified N-deacetylated derivative of chitin. Recently, much attention has been paid to chitosan as a potential polysaccharide resource. It has become of great interest since it is inexhaustible, and also as a new functional material of high potential in various fields and recent progress in chitin and chitosan chemistry is quite noteworthy. Chitosan is obtained by deacetylation of chitin using strong alkali solutions. Both polymers are biodegradable, biocompatible and have many biological, biomedical, agriculture and technical applications.The potential applications of chitosan and chitin can be extremely enlarged by conducting chemical modifications using the OH and the NH2 groups. Examples of these modifications are acylation, alkylation, carboxymethylation and grafting.