Mucoadhesive drug delivery systems are of great interest due to the fate of prolonging residence time at the site of absorption/action (I), providing sustained drug release (II), and minimizing drug degradation in the body (III). Various natural, semi-synthetic, and synthetic polymers have been used in the development of mucoadhesive drug delivery systems. Chitosan – a naturel cationic polysaccharide – exhibiting mucoadhesive features, is widely used in the development of mucoadhesive drug delivery systems. Nevertheless, chitosan per se shows some drawbacks as its limitation in mucoadhesive strength, limited water solubility, and pH burden. Therefore, modification of chitosans has been investigated to overcome these limitations. In this chapter, we focus on the concept of mucoadhesion with theories showing the beneficial modifications of chitosan for different body sites such as ocular and vaginal mucosae as well as in wound management.