Chitosan is the deacetylated form of chitin. Generally, the substance becomes soluble in dilute acids when the degree of deacetylation is more than 50%. The solubility of chitosan in dilute acids is often needed to be modified when specific drug release properties have to be tailored into the dosage form. The available toxicological data on chitosan and its modified forms appears to indicate its safety for oral use because high doses have been found to be tolerated well in rodents and rabbits. However, its local action as a haemostatic together with its ability to activate macrophages and cause cytokine release may require a careful assessment of its safety for parenteral use. This book offers the dynamics of chitosan's detailed composition.