**Abstract**

Oral delivery is the most common and preferred route of drug administration due to its convenience and ease of administration. However, various factors such as poor solubility, low dissolution rate, stability, and bioavailability of many drugs remain an ongoing challenge in achieving desired therapeutic levels. The delivery of drugs must overcome various obstacles, including the acidic gastric environment, the presence of the intestinal efflux and influx transporters and the continuous secretion of mucus that protects the gastrointestinal tract (GIT). As the number and chemical diversity of drugs has increased, various strategies are required to develop orally active therapeutics. One of the approaches is to use chitosan as a carrier for oral delivery of peptides, proteins as well as vaccines delivery. Chitosan, a non-toxic N-deacetylated derivative of chitin appears to be under intensive progress during the last years towards the development of safe and efficient chitosan-based drug delivery systems. This polymer has been recognised as a versatile biomaterial because of its biodegradability, biocompatibility, and non-toxicity. This chapter reviews the physicochemical characteristics of chitosan and the strategies that have been successfully applied to improve oral proteins, peptides, and vaccines bioavailability, primarily through various formulation strategies.

**Keywords:** chitin, chitosan, bioavailability, oral delivery, peptides, vaccines
