This document discusses mucoadhesive drug delivery systems. It begins by defining mucoadhesive drug delivery as a system that uses the bioadhesive properties of water-soluble polymers to target and extend the release of a drug to a specific body region. The advantages include increased bioavailability and drug targeting. Various types of mucoadhesive systems are described, including those for oral, nasal, vaginal, and rectal administration. In particular, buccal drug delivery systems and their advantages over other routes are discussed in detail. The document also covers permeation mechanisms, enhancers, and the structures of different mucosa.