In case of targeting the drug to the desired part of the skin, vehicles play an important role beside the characteristics of the drug. Many natural and synthetic vehicles have been used for various topical dermal/transdermal preparations. However, chitosan has been standing out with its many advantages based mainly on its biological and physicochemical properties. Chitosan is a unique hydrophilic biopolymer obtained by partial deacetylation of chitin, which is one of the most abundant polysaccharides. It is a natural product widely found in crustacean shells, fungal cell walls, insect exoskeletons, and mollusks. Chitosan is a linear glycosaminoglycan made up of N-acetyl-D-glucosamine units. This book focuses on the use of chitosan for dermal/transdermal drug delivery systems following a general overview of chitosan.