In recent years, environmental pollution with heavy metal ions has attracted the attention of many research groups world wide. Contamination with these heavy metal ions has also increased public concerns because of their toxicities in relatively low concentration, their non biodegradable nature and tendency of bioaccumulation. The increasing demand for the recovery of these metals from industrial effluents has stressed the development and the testing of new sorbing materials including use of abundant waste biomaterials. For last three to four decades, biopolymers have been extensively studied because of their interactions with metal ions. Cellulosics, chitin and chitosans are the most widely studied and reported biopolymers for metal ion sorption. Chitin is the main structural component of the exoskeleton of crustaceans (e.g., crabs, prawns, crabs, insects and shrimps) and the cell walls of fungi. Chitin is a polymer made up of acetylglucosamine units. In the case of some Mucorales species, chitin is replaced by chitosan, a polymer made up of glucosamine units. Chitosan is commercially produced by the deacetylation of chitin and is a typical biopolymer with excellent properties for the uptake of metal ions. Metal cations can be adsorbed by chelation on amine and hydroxyl groups of chitosan in near neutral solutions. In the case of metal anions, the sorption proceeds by electrostatic attraction on protonated amine groups in acidic solutions. However, the presence of ligands and the pH strongly control sorption performance and the uptake mechanism. Several examples are discussed with heavy metals like Cu, Zn, Ni, Cr and toxic metals like Pb, Hg and Cd. Sorption performance is also controlled by other structural parameters of the polymer (degree of deacetylation and crystallinity) that control swelling and diffusion properties of chitosan. The identification of the factors affecting sorption process helps in designing new derivatives of chitosan. Sorption properties may be improved by physical modification of chitosan including manufacturing gel beads and decreasing crystallinity. Selectivity and reusability can be enhanced by chemical modification like grafting and crosslinking. Several examples are discussed to demonstrate the versatility of the material. This versatility allows the polymer to be used under different forms ranging from water soluble form to solid form, gels, fibers and hollow fibers. These interactions of metal ions with chitosan can be used for the decontamination of effluents, for the recovery of valuable metals and also for the development of new materials or new processes involving metal-loaded chitosan. Several examples are cited in the design of new sorbing materials.