Chitin is an unbranched polymer of ?(1?4)-N-acetyl-D-glucosamine, and chitosan is deacetylated chitin derivatives. These polysaccharides are widely distributed in the shells of crustacea (lobster, crab, and shrimp), in the cuticles of insects, in the shells and skeletons of mollusks and in the cell walls of fungi. The shells of crab, shrimp and lobster, which are currently waste materials of the food processing industries, are the best available sources of chitin and chitosan. Due to their unique biological, physicochemical properties and abundance, chitin and chitosan have been found to have many exciting potential applications in medicine, food, and in wastewater treatment. The environmental applications of chitin and chitosan for clarifying water, recovering proteinaceous materials, removing lipids, grease, pesticides, PCB, toxic heavy metals and textile dye residues from industrial effluents and polluted water bodies have been reviewed. Some recent results on the mechanisms and kinetics for the adsorption of textile dyes on chitin have also been reported. The adsorption results showed that chitin adsorbs up to 7% of its weight in an azo dye, Orange (II), because of the interaction between the positively charged acetamido/amino groups in chitin/chitosan and negatively charge functional groups in the dyes. The data presented suggest that the application of chitin could solve several environmental problems at once for aquaculture, shellfishing and other industries.