This chapter reviews the role of a natural polysaccharide— chitosan and chitosan-based nano-dosage forms— targeted against infectious diseases. Nano delivery systems carrying an antimicrobial payload can increase the overall efficacy of drugs by virtue of their increased surface-to-volume ratio. Microbial diseases, once the greatest cause of death and disability, had almost lost their bite after the discovery of penicillin. The occurrence of both emerging and re-emerging infectious diseases has substantially increased. Due to the development of antibiotic resistance, infections may now become lethal. Chitosan— a polysaccharide obtained from natural sources— was found to have antimicrobial properties and be particularly suitable for the development of nanovehicles for antimicrobial drugs. A variety of nano-dosage forms have been developed and evaluated by a host of researchers using almost every conceivable biomolecule. Chitosan has broad spectrum of antimicrobial activity and is equipped with in-built hydroxyl and amino groups that can be attached to drugs with simple chemical reactions. Its antimicrobial properties have already been exploited in wound healing.