The development of heterogeneous catalytic systems for carrying out liquid phase chemical and biochemical transformations is a major area of research, which has great significance for the development of cleaner and more efficient processes. This review reflects the growing significance of renewable polymeric supports for such catalysts. The focus of this review is chitosan, a material produced in enormous quantities each year and derived predominantly from the shells of crustaceans. This material has many benefits, some of which have hardly been exploited in catalysis. A survey of methodology for the functionalization of chitosan, and how the functional chitosans are used in catalysis, is given.